Three dimensional printer with composite filament fabrication

ABSTRACT

Various embodiments related to three dimensional printers, and reinforced filaments, and their methods of use are described. In one embodiment, a void free reinforced filament is fed into an conduit nozzle. The reinforced filament includes a core, which may be continuous or semi-continuous, and a matrix material surrounding the core. The reinforced filament is heated to a temperature greater than a melting temperature of the matrix material and less than a melting temperature of the core prior to drag the filament from the conduit nozzle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. Nos. 14/333,881 and 14/333,947, both filed on Jul. 17, 2014, andeach of which claims the benefit under 35 U.S.C. §119(e) of U.S.provisional application Ser. Nos. 61/804,235, filed Mar. 22, 2013;61/815,531, filed Apr. 24, 2013; 61/831,600, filed Jun. 5, 2013;61/847,113, filed Jul. 17, 2013; 61/878,029, filed Sep. 15, 2013;61/880,129, filed Sep. 19, 2013; 61/881,946, filed Sep. 24, 2013;61/883,440, filed Sep. 27, 2013; 61/902,256, filed Nov. 10, 2013, and61/907,431, filed Nov. 22, 2013, the disclosures of which are hereinincorporated by reference in their entirety; and is a continuation inpart of each of U.S. patent application Ser. No. 14/222,318, filed Mar.21, 2014 and Ser. No. 14/297,437, filed Jun. 5, 2014, the disclosures ofwhich are herein incorporated by reference in their entirety.

FIELD

Aspects relate to three dimensional printing.

BACKGROUND

Since the initial development of three dimensional printing, also knownas additive manufacturing, various types of three dimensional printingand printers for building a part layer by layer have been conceived. Forexample, Stereolithography (SLA) produces high-resolution parts.However, parts produced using SLA typically are not durable and are alsooften not UV-stable and instead are typically used for proof-of-conceptwork. In addition to SLA, Fused Filament Fabrication (FFF) threedimensional printers are also used to build parts by depositingsuccessive filament beads of acrylonitrile butadiene styrene (ABS), or asimilar polymer. In a somewhat similar technique, “towpregs” includingcontinuous fiber reinforced materials including a resin are deposited ina “green state”. Subsequently, the part is placed under vacuum andheated to remove entrapped air voids present in the deposited materialsand fully cure the part. Another method of additive manufacturing,though not considered three-dimensional printing, includespreimpregnated (prepreg) composite construction where a part is made bycutting sheets of fabric impregnated with a resin binder intotwo-dimensional patterns. One or more of the individual sheets are thenlayered into a mold and heated to liquefy the binding resin and cure thefinal part. Yet another method of (non-three-dimensional printing)composite construction is filament winding which uses strands ofcomposite (containing hundreds to thousands of individual carbon strandsfor example) that are wound around a custom mandrel to form a part.Filament winding is typically limited to convex shapes due to thefilaments “bridging” any concave shape due to the fibers being undertension and the surrounding higher geometry supporting the fibers sothat they do not fall into the underlying space.

SUMMARY

In one embodiment, a method for manufacturing a part includes: feeding avoid free core reinforced filament into an conduit nozzle, wherein thecore reinforced filament comprises a core and a matrix materialsurrounding the core; heating the core reinforced filament to atemperature greater than a melting temperature of the matrix materialand less than a melting temperature of the core; and extruding the corereinforced filament to form the part.

In another embodiment, a filament for use with a three dimensionalprinter includes a multistrand core and a matrix material surroundingthe multistrand core. The matrix material is substantially impregnatedinto the entire cross-section of the multistrand core, and the filamentis substantially void free.

In yet another embodiment, a method for manufacturing a part, the methodincludes: feeding a filament into a heated conduit nozzle and cuttingthe filament at a location at or upstream from an outlet of the heatednozzle.

In another embodiment, a three dimensional printer includes a heatedconduit nozzle including a conduit nozzle eyelet or outlet and a feedingmechanism constructed and arranged to feed a filament into the heatedconduit nozzle. The three dimensional printer also includes a cuttingmechanism constructed and arranged to cut the filament at a location at,or upstream from, the heated conduit nozzle eyelet or outlet.

In yet another embodiment, a heated conduit nozzle includes a nozzleinlet constructed and arranged to accept a filament and a conduit nozzleeyelet or outlet in fluid communication with the nozzle inlet. Across-sectional area of the conduit nozzle eyelet or outlet transverseto a path of the filament is larger than a cross-sectional area of thenozzle inlet transverse to the path of the filament.

In another embodiment, a filament for use with a three dimensionalprinter includes a core including a plurality of separate segmentsextending in an axial direction of the filament and a matrix materialsurrounding the plurality of segments. The matrix material issubstantially impregnated into the entire cross-section of the core, andthe filament is substantially void free.

In yet another embodiment, a method includes: positioning a filament ata location upstream of a conduit nozzle eyelet or outlet where atemperature of the conduit nozzle eyelet is below the meltingtemperature of the filament; and displacing the filament out of theconduit nozzle eyelet or outlet during a printing process.

In another embodiment, a method includes: feeding a filament from afirst channel sized and arranged to support the filament to a cavity influid communication a conduit nozzle eyelet or outlet, wherein across-sectional area of the cavity transverse to a path of the filamentis larger than a cross-sectional area of the first channel transverse tothe path of the filament.

In yet another embodiment, a method for forming a filament includes:mixing one or more fibers with a first matrix material to form a corereinforced filament; and passing the filament through a circuitous pathto impregnate the first matrix material into the one or more fibers.

In another embodiment, a method includes: coextruding a core reinforcedfilament and a coating matrix material to form an outer coating on thecore reinforced filament with the coating material.

In yet another embodiment, a method for manufacturing a part includes:feeding a filament into a heated conduit nozzle; extruding the filamentfrom a conduit nozzle eyelet or outlet; and applying a compressive forceto the extruded filament with the conduit nozzle eyelet.

In another embodiment, a method for manufacturing a part includes:depositing a first filament into a layer of matrix material in a firstdesired pattern using a printer head; and curing at least a portion ofthe matrix layer to form a layer of a part including the deposited firstfilament.

It should be appreciated that the foregoing concepts, and additionalconcepts discussed below, may be arranged in any suitable combination,as the present disclosure is not limited in this respect. Further, otheradvantages and novel features of the present disclosure will becomeapparent from the following detailed description of various non-limitingembodiments when considered in conjunction with the accompanyingfigures.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures may be represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIG. 1 is a schematic representation of a three dimensional printingsystem using a continuous core reinforced filament;

FIG. 2 is a representative flow chart of a three dimensional printingprocess;

FIG. 3A is a schematic representation of a continuous core reinforcedfilament including a solid continuous core and surrounding thermoplasticresin with a smaller proportion of solid continuous core;

FIG. 3B is a schematic representation of a continuous core reinforcedfilament including a solid continuous core surrounded by thermoplasticresin with a larger proportion of solid continuous core;

FIG. 3C is a schematic representation of a continuous core reinforcedfilament including a multistrand continuous core surrounded bythermoplastic resin with a smaller proportion of the multistrandcontinuous core;

FIG. 3D is a schematic representation of a continuous core reinforcedfilament including a multistrand continuous core surrounded bythermoplastic resin with a large proportion of the multistrandcontinuous core;

FIG. 3E is a schematic representation of a continuous core reinforcedfilament including a multistrand continuous core including elements withelectrical, optical, or fluidic properties;

FIG. 4 is a schematic representation a prior art towpreg including greenmatrix resin particles or resin strands combined with is a schematicrepresentation of a prophetic example of a nozzle and a propheticexample of an extruded towpreg including voids;

FIG. 5 is a schematic representation of fiber strand bunching within aprophetic nozzle;

FIG. 6A is a schematic representation of a divergent conduit nozzleeyelet utilized in some embodiments of the printing system;

FIG. 6B is a schematic representation of a straight conduit nozzleeyelet utilized in some embodiments of the printing system;

FIG. 6C is a schematic representation of a rounded tip conduit nozzleeyelet utilized in some embodiments of the printing system;

FIG. 7 is a schematic representation of a prior art three dimensionalprinting system;

FIG. 8 is a schematic representation of a three dimensional printingsystem including a cutting mechanism and a printing process bridging anopen space;

FIG. 9 is a schematic representation of a part formed by thethree-dimensional printing system and/or process that includes anenclosed open space;

FIG. 10 is a schematic representation of a three-dimensional printingsystem including a guide tube;

FIG. 11 is a photograph of a three dimensional printing system includinga guide tube;

FIG. 12A is a schematic representation of a shear cutting head withoptional indexing positions;

FIG. 12B is a schematic representation of the shear cutting head of FIG.11A in a second indexing position;

FIG. 13 is a schematic representation of a multi-conduit nozzle printhead including shear cutting;

FIG. 14A is a schematic representation of a conduit nozzle;

FIG. 14B is a schematic representation of a conduit nozzle having arounded eyelet or outlet;

FIG. 14C is a schematic representation of another conduit nozzle havinga rounded eyelet or outlet;

FIG. 15A is a schematic cross-sectional view of a cutting mechanismintegrated with a conduit nozzle eyelet or outlet tip;

FIG. 15B is a schematic cross-sectional view of the cutting mechanismintegrated with a conduit nozzle eyelet or outlet tip depicted in FIG.14A rotated 90°;

FIG. 15C is a bottom view of one embodiment of a cutting mechanismintegrated with a conduit nozzle eyelet or outlet tip;

FIG. 15D is a bottom view of one embodiment of a cutting mechanismintegrated with a conduit nozzle eyelet or outlet tip;

FIG. 16 is a schematic cross-sectional view of a cutting mechanismintegrated with a conduit nozzle eyelet or outlet tip;

FIG. 17A is a schematic representation of a three-dimensional printingsystem applying a compaction pressure during part formation;

FIG. 17B is a schematic representation of a continuous core reinforcedfilament to be utilized with the printing system prior to deposition;

FIG. 17C is a schematic representation of the continuous core reinforcedfilament and surrounding beads of materials after deposition usingcompaction pressure;

FIG. 18A is a schematic representation of a prior art nozzle;

FIG. 18B is a schematic representation of a divergent nozzle;

FIG. 18C is a schematic representation of the divergent nozzle of FIG.18B shown in a feed forward cleaning cycle;

FIG. 19A is a schematic representation of a continuous core filamentbeing printed with a straight conduit nozzle;

FIG. 19B is a schematic representation of a green towpreg being printedwith a straight conduit nozzle;

FIGS. 19C-19E are schematic representations of a continuous corefilament being stitched and printed with a divergent conduit nozzle;

FIG. 20A is a schematic representation of a multi-material conduitnozzle with a low friction cold feeding zone;

FIG. 20B is a schematic representation of a slightly convergent conduitnozzle including a low friction cold feeding zone;

FIG. 21A is a schematic representation of a prior art nozzle;

FIGS. 21B-21D represent various embodiments of nozzle geometries;

FIG. 22 is a schematic representation of an anti-drip deposition headand pressure reduction system;

FIG. 23A is a schematic representation of a semi-continuous corefilament positioned within deposition head;

FIG. 23B is a schematic representation of a semi-continuous corefilament with overlapping strands positioned within deposition head;

FIG. 23C is a schematic representation of a semi-continuous corefilament with aligned strands and positioned within deposition head;

FIG. 24A is a schematic representation of a multistrand continuous core;

FIG. 24B is a schematic representation of a semi-continuous corefilament with offset strands;

FIG. 24C is a schematic representation of a semi-continuous corefilament with aligned strands;

FIG. 24D is a schematic representation of a semi-continuous corefilament with aligned strands and one or more continuous strands;

FIG. 25 is a schematic representation of a fill pattern using asemi-continuous core filament;

FIG. 26 is a schematic representation of multiple printed layers formedby the three-dimensional printing system and/or process with thedifferent layers and different portions of the layers includingdifferent fiber directions;

FIG. 27A is a schematic representation of a three dimensional printingprocess for forming a component in a first orientation;

FIG. 27B is a schematic representation of a fixture to use with the partof FIG. 27A;

FIG. 27C is a schematic representation of a three dimensional printingprocess for forming a component on the part of FIG. 27A in a secondorientation;

FIG. 28A is a schematic representation of a three dimensional printingprocess using a multiaxis system in a first orientation;

FIG. 28B is a schematic representation of forming a component in anotherorientation on the part of FIG. 28A;

FIG. 29 is a schematic representation of a three dimensional printingsystem using a continuous core reinforced filament;

FIG. 30A is a schematic representation of a part including a shellapplied to the sides using a three dimensional printing process;

FIG. 30B is a schematic representation of a part including a shellapplied to the top and sides using a three-dimensional printing process;

FIG. 30C is a schematic representation of a part including a shell thathas been offset from an underlying supporting surface;

FIG. 30D is a schematic representation of a part formed with a fillmaterial;

FIG. 30E is a schematic representation of a part formed with compositematerial extending inwards from the corners and polymer fill in theinterior;

FIG. 30F is a schematic representation of a part formed with compositematerial extending inwards from the corners and polymer fill in theinterior;

FIG. 30G is a schematic representation of a part formed with compositematerial extending inwards from the corners and polymer fill in theinterior;

FIG. 31A is a schematic representation of an airfoil formed withdiscrete subsections including fiber orientations in the same direction;

FIG. 31B is a schematic representation of an airfoil formed withdiscrete subsections including fiber orientations in differentdirections;

FIG. 31C is a schematic representation of an airfoil formed withdiscrete subsections and a shell formed thereon;

FIG. 32 is a schematic representation of a three dimensional printingsystem including a print arm and selectable printer heads;

FIG. 33 is a schematic representation of a multi-element printer headfor use in the printing system;

FIG. 34 is a schematic representation of a stereolithography threedimensional printing process including deposited reinforcing fibers;

FIG. 35 is a schematic representation of a stereolithography threedimensional printing process including deposited reinforcing fibers;

FIG. 36 is a schematic representation of a three dimensional printedpart including incorporated printed components with differentfunctionalities;

FIG. 37 is a schematic representation of a three dimensional printingsystem being used to form multiple layers in a printed circuit board;

FIG. 38 is a schematic representation of a three dimensional printingsystem being used to fill various voids in a printed circuit board withsolder or solder paste;

FIG. 39 is a schematic representation of the print circuit board of FIG.38 after the formation of vias and contact pads;

FIG. 40A is a schematic representation of a printed part including ahole drilled therein;

FIG. 40B is a schematic representation of a printed part including areinforced hole formed therein;

FIG. 40C is a schematic representation of a printed part including areinforced hole formed therein;

FIG. 41A is a schematic representation of a composite part formed usingthree-dimensional printing methods; and

FIG. 41B is a scanning electron microscope image of a reinforcing carbonfiber and perpendicularly arranged carbon nanotubes;

FIG. 42 is a schematic representation of a circuitous path impregnationsystem

FIG. 43A is a schematic representation of an incoming material withcomingled tows;

FIG. 43B is a schematic representation of the material of FIG. 43A afterimpregnation;

FIG. 44A is a schematic representation of an offset roller impregnationsystem;

FIG. 44B is a schematic representation of the roller impregnation systemof FIG. 44A in an optional loading configuration;

FIG. 45 is a schematic representation of an impregnation system combinedwith a vacuum impregnation nozzle;

FIG. 46 is a schematic representation of an impregnation systemintegrated with a printing nozzle;

FIG. 47 is a schematic representation of a printing nozzle including acircuitous path impregnation system;

FIG. 48 is a schematic representation of a multi-nozzlethree-dimensional printer;

FIG. 49A is a schematic representation of a co-extrusion process to forma continuous core reinforced filament and an optional outer coating;

FIG. 49B is a schematic representation of a starting material used inthe process depicted in FIG. 49A;

FIG. 49C is a schematic representation of a starting material used inthe process depicted in FIG. 49A;

FIG. 49D is a schematic representation of one embodiment of a materialafter impregnation using the process depicted in FIG. 49A;

FIG. 49E is a schematic representation of one embodiment of a materialafter impregnation using the process depicted in FIG. 49A;

FIG. 49F is a schematic representation of one embodiment of a materialafter impregnation using the process depicted in FIG. 49A;

FIG. 49G is a schematic representation of one embodiment of a materialincluding an optional outer coating using the process depicted in 49A;

FIG. 49H is a schematic representation of one embodiment of a materialincluding an optional outer coating using the process depicted in 49A;

FIG. 49I is a schematic representation of one embodiment of a materialincluding an optional outer coating using the process depicted in 49A;

FIG. 50A is a schematic representation of a co-extrusion process to forma continuous core reinforced filament and an optional outer coating;

FIG. 50B is a schematic representation of a starting material used inthe process depicted in FIG. 50A;

FIG. 50C is a schematic representation of a starting material used inthe process depicted in FIG. 49A;

FIG. 50D is a schematic representation of a starting material afterbeing spread out using the process depicted in FIG. 50A;

FIG. 50E is a schematic representation of one embodiment of a materialafter impregnation using the process depicted in FIG. 50A;

FIG. 50F is a schematic representation of one embodiment of a materialafter shaping using the process depicted in FIG. 50A;

FIG. 50G is a schematic representation of one embodiment of a materialafter shaping using the process depicted in FIG. 50A;

FIG. 50H is a schematic representation of one embodiment of a materialafter shaping using the process depicted in FIG. 50A; and

FIG. 50I is a schematic representation of one embodiment of a materialincluding an optional outer coating using the process depicted in 50A.

DETAILED DESCRIPTION

The inventors have recognized that one of the fundamental limitationsassociated with typical additive manufacturing methods is the strengthand durability of the resulting part. For example, Fused FilamentFabrication results in a part exhibiting a lower strength than acomparable injection molded part. This reduction in strength may be dueto weaker bonding between the adjoining strips of deposited material (aswell as air pockets and voids) as compared to the continuous andsubstantially void free material formed, for example, during injectionmolding. The inventors have also recognized that the prepreg compositeconstruction methods using a sheet-based approach to form a threedimensional part are both time consuming and difficult to handleresulting in higher expenses. Further, bending such sheets aroundcurves, a circle for example, may cause the fibers to overlap, buckle,and/or distort resulting in undesirable soft spots in the resultantcomponent. With regards to three dimensional printers using “towpregs”or “tows” including reinforcing fibers and a resin, the inventors havenoted that the prior art deposited materials are often difficult to loadin the machine, and further difficult to feed through the print head,due to their extremely flexible, and usually high-friction (sticky)initial state. Further, these green materials tend to entrap air andinclude air voids. Thus, without a subsequent vacuum and heating step,the resultant part also contains voids, and is substantially weaker thana traditional composite part constructed under a vacuum. Therefore, theadditional steps associated with preparing a towpreg slow down theprinting process and result in the entrapment of ambient air.

Due to the limitations associated with typical three dimensionalprinting systems noted above, the inventors have recognized a need toimprove the strength of three dimensional printed composites. Further,there is a need for additive manufacturing construction techniques thatallow for greater speed; removal or prevention of entrapped air in thedeposited material; reduction of the need for subsequent vacuumingsteps; and/or correct and accurate extrusion of the composite corematerial. The inventors have also recognized that it is desirable toprovide the ability to deposit fibers in concave shapes, and/orconstruct discrete features on a surface or composite shell.

In view of the above, the inventors have recognized the benefitsassociated with providing a three dimensional printing system thatprints structures using a substantially void-free preimpregnated(prepreg) material, or that is capable of forming a substantially voidfree material for use in the deposition process. For example, in oneembodiment, a three dimensional printer uses a continuous corereinforced filament including a continuous multistrand core materialwith multiple continuous strands that are preimpregnated with athermoplastic resin that has already been “wicked” into the strands,such a preimpregnated material is then used to form a three dimensionalstructure. Due to the thermoplastic resin having already wicked into thestrands, the material is not “green” and is also rigid, low-friction,and substantially void free. In another embodiment, a solid continuouscore is used and the thermoplastic resin wets the solid continuous coresuch that the resulting continuous core reinforced filament is alsosubstantially void free. Additionally, embodiments in which asemi-continuous core is used in which a core extending through thelength of a material is sectioned into a plurality of portions along thelength is also contemplated. Such an embodiment may include either asolid core or multiple individual strands that are either evenly spacedfrom one another or include overlaps as the disclosure is not solimited. In either case, such a core material may also be preimpregnatedor wetted as noted above. A substantially void free material may have avoid percentage that is less than about 1%, 2%, 3%, 4%, 5%, 10%, 13%, orany other appropriate percentage. For example, the void free materialmay have a void percentage that is between about 1% and 5%.Additionally, due to the processing methods described below, partsprinted using the above-noted void free material may also exhibit voidpercentages less than about 1%, 2%, 3%, 4%, 5%, 10%, or 13%.

While preimpregnated materials are discussed above, in one embodiment, asolid continuous core filament may be selectively combined with a resinin a nozzle eyelet or outlet. Due to the regular and well-definedgeometry of the solid core, the resin may evenly coat the core and theresulting deposited composite material is substantially free from voids.

Within this application, core reinforced filaments are described asbeing either impregnated or wetted. For example, a solid core might belet with a matrix material, or a multistrand core may be bothimpregnated and fully wet with a matrix material. However, for thepurposes of this application, a filament including a core that has beenimpregnated should be understood to refer to a filament including a corethat has been fully impregnated and/or wet with matrix material. Aperson of ordinary skill would be able to understand how this might beinterpreted for applications where a core material is a solid core.

In addition to the above, a core reinforced material as describedthroughout this application. For specific embodiments and examples, acontinuous core and/or a semi-continuous core might be described forexemplary purposes. However, it should be understood that either acontinuous and/or a semi-continuous core might be used in any particularapplication and the disclosure is not limited in this fashion.Additionally, with regards to a core reinforced material, the core mayeither be positioned within an interior of the filament or the corematerial may extend to an exterior surface of the filament as thedisclosure is not limited in this fashion. Additionally, it should beunderstood that a court reinforced material also includes reinforcementsprovided by materials such as optical materials, fluid conductingmaterials, electrically conductive materials as well as any otherappropriate material as the disclosure is not so limited.

In yet another embodiment, the inventors have recognized the benefitsassociated with providing a continuous or semi-continuous core combinedwith stereolithography (SLA), selective laser sintering (SLS), and otherthree dimensional printing processes using a matrix in liquid or powderform to form a substantially void free parts exhibiting enhancedstrength. The above embodiments may help to reduce, or eliminate, theneed for a subsequent vacuum step as well as improve the strength of theresulting printed structures by helping to reduce or eliminate thepresence of voids within the final structure.

In addition to improvements in strength due to the elimination of voids,the inventors have recognized that the current limitation of laying downa single strip at a time in three dimensional printing processes may beused as an advantage in composite structure manufacturing. For example,the direction of reinforcing materials deposited during the printingprocess within a structure may be controlled within specific layers andportions of layers to control the directional strength of the compositestructure both locally and overall. Consequently, the directionality ofreinforcement within a structure can provide enhanced part strength indesired locations and directions to meet specific design requirements.The ability to easily tailor the directional strength of the structurein specific locations may enable both lighter and stronger resultingparts.

In embodiments, it may be desirable to include a cutting mechanism withthe three dimensional printing system. Such a cutting mechanism may beused to provide selective termination in order to deposit a desiredlength of material. Otherwise, the printing process could not be easilyterminated due to the deposited material still being connected to thematerial within the deposition head, for example, a continuous core. Thecutting mechanism may be located at the outlet of the associated printerconduit nozzle or may be located upstream from the outlet. Further, insome embodiments, the cutting mechanism is located between a feedingmechanism for the core material and the outlet of the conduit nozzle.However regardless of the specific configuration and location, thecutting mechanism enables the three dimensional printing system toquickly and easily deposit a desired length of material in a desireddirection at a particular location. In contrast, systems which do notinclude a cutting mechanism continuously deposit material until thematerial runs out or it is manually cut. This limits both the complexityof the parts that can be produced, the speed of the printing process aswell as the ability to deposit the material including the continuouscore in a particular direction. Depending on the embodiment, the cuttingmechanism may also interrupt the printer feed by blocking the conduitnozzle or preventing the feeding mechanism from applying force orpressure to a portion of the material downstream from the cuttingmechanism. While in some cases it may be desirable to include a cuttingmechanism with the three dimensional printer, it should be understoodthat embodiments described herein may be used both with and without acutting mechanism as the current disclosure is not limited in thisfashion. Further, a cutting mechanism may also be used with embodimentsthat do not include a continuous core.

It should be understood that the substantially void free materialdescribed herein may be manufactured in any number of ways. However, inone embodiment, the material is formed by applying a varying pressureand/or forces in different directions during formation of the material.For example, in one embodiment, multiple strands of a polymer or resinand a core including a plurality of reinforcing fibers are co-mingledprior to feeding into a system. The system then heats the materials to adesired viscosity of the polymer resin and applies varying pressuresand/or forces in alternating directions to the comingled towpreg to helpfacilitate fully impregnating the fibers of the towpreg with the polymeror resin. This may be accomplished using a smooth circuitous pathincluding multiple bends through which a green towpreg is passed, or itmay correspond to multiple offset rollers that change a direction of thetowpreg as it is passed through the system. As the towpreg passesthrough this circuitous path, the varying forces and pressures help tofully impregnate the polymer into the core and form a substantially voidfree material. While a co-mingled towpreg including separate strands ofreinforcing fibers and polymer resin are described above, embodiments inwhich a solid core and/or multiple reinforcing fibers are comingled withpolymer particles, or dipped into a liquid polymer or resin, and thensubjected to the above noted process are also contemplated. In additionto the above, after impregnating the core with the polymer, thesubstantially void free material may be fed through a shaping nozzle toprovide a desired shape. The nozzle may be any appropriate shapeincluding a circle, an oval, a square, or any other desired shape. Whilea continuous core is noted above, embodiments in which a semi-continuouscore is used are also contemplated. Additionally, this formation processmay either be performed under ambient conditions, or under a vacuum tofurther eliminate the presence of voids within the substantially voidfree material.

In some embodiments, it may be desirable to provide a smooth outercoating on a towpreg corresponding to the substantially void freematerial noted above. In such an embodiment, a substantially void freematerial, which is formed as noted above, or in any other appropriateprocess, is co-extruded with a polymer through an appropriately shapednozzle. As the substantially void free material and polymer are extrudedthrough the nozzle, the polymer forms a smooth outer coating around thesubstantially void free material.

The materials used with the currently described three dimensionalprinting processes may incorporate any appropriate combination ofmaterials. For example appropriate resins and polymers include, but arenot limited to, acrylonitrile butadiene styrene (ABS), epoxy, vinyl,nylon, polyetherimide (PEI), Polyether ether ketone (PEEK), PolyacticAcid (PLA), Liquid Crystal Polymer, and various other thermoplastics.The core may also be selected to provide any desired property.Appropriate core fiber or strands include those materials which impart adesired property, such as structural, conductive (electrically and/orthermally), insulative (electrically and/or thermally), optical and/orfluidic transport. Such materials include, but are not limited to,carbon fibers, aramid fibers, fiberglass, metals (such as copper,silver, gold, tin, steel), optical fibers, and flexible tubes. It shouldbe understood that the core fiber or strands may be provided in anyappropriate size. Further, multiple types of continuous cores may beused in a single continuous core reinforced filament to provide multiplefunctionalities such as both electrical and optical properties. Itshould also be understood that a single material may be used to providemultiple properties for the core reinforced filament. For example, asteel core might be used to provide both structural properties as wellas electrical conductivity properties.

In some embodiments, in addition to selecting the materials of the corereinforced filament, it is desirable to provide the ability to use corereinforced filaments with different resin to reinforcing core ratios toprovide different properties within different sections of the part. Forexample, a low-resin filler may be used for the internal construction ofa part, to maximize the strength-to-weight ratio (20% resin by crosssectional area, for example). However, on the outer cosmetic surface ofthe part, a higher, 90% resin consumable may be used to prevent thepossible print through of an underlying core or individual fibercontinuous of the core. Additionally, in some embodiments, theconsumable material may have zero fiber content, and be exclusivelyresin. Therefore, it should be understood that any appropriatepercentage of resin may be used.

The core reinforced filaments may also be provided in a variety ofsizes. For example, a continuous or semi-continuous core reinforcedfilament may have an outer diameter that is greater than or equal toabout 0.001 inches and less than or equal to about 0.4 inches. In onespecific embodiment, the filament is greater than or equal to about0.010 inches and less than or equal to about 0.030 inches. In someembodiments, it is also desirable that the core reinforced filamentincludes a substantially constant outer diameter along its length.Depending on the particular embodiment, different smoothnesses andtolerances with regards to the core reinforced filament outer diametermay be used. A constant outer diameter may help to provide constantmaterial flow rate and uniform properties in the final part.

As described in more detail below, the ability to selectively printelectrically conductive, optically conductive, and/or fluidly conductivecores within a structure enables the construction of desired componentsin the structure. For example, electrically conductive and opticallyconductive continuous cores may be used to construct strain gauges,optical sensors, traces, antennas, wiring, and other appropriatecomponents. Fluid conducting cores might also be used for formingcomponents such as fluid channels and heat exchangers. The ability toform functional components on, or in, a structure offers multiplebenefits. For example, the described three dimensional printingprocesses and apparatuses may be used to manufacture printed circuitboards integrally formed in a structure; integrally formed wiring andsensors in a car chassis or plane fuselage; as well as motor cores withintegrally formed windings to name a few.

Turning now to the figures, specific embodiments of the disclosedmaterials and three dimensional printing processes are described.

FIG. 1 depicts an embodiment of a three dimensional printer usingcontinuous strands of composite material to build a structure. In thedepicted embodiment, the continuous strand of composite material is acontinuous core reinforced filament 2. The continuous core reinforcedfilament 2 comprises a towpreg that is substantially void free andincludes a polymer 4 that coats or impregnates an internal continuouscore 6. Depending upon the particular embodiment, the core 6 may be asolid core or it may be a multistrand core including multiple strands.

The continuous core reinforced filament 2 is fed through a heateddeposition head, such as conduit nozzle 10 (in some embodiments, asdescribed below, dragged or pulled through). As the continuous corereinforced filament is fed through the conduit nozzle it is heated to apreselected deposition temperature. This temperature may be selected toeffect any number of resulting properties including, but not limited to,viscosity of the deposited material, bonding of the deposited materialto the underlying layers, and the resulting surface finish. While thedeposition temperature may be any appropriate temperature, in oneembodiment, the deposition temperature is greater than the meltingtemperature of the polymer 4, but is less than the decompositiontemperature of the resin and the melting or decomposition temperature ofthe core 6. Any suitable heater may be employed to heat the depositionhead, such as a band heater or coil heater.

After being heated in the heated conduit nozzle 10, the continuous corereinforced filament 2 is deposited onto a build platen 16 to buildsuccessive layers 14 to form a final three dimensional structure. Theposition of the heated conduit nozzle 10 relative to the build platen 16during the deposition process may be controlled in any appropriatefashion. For example, the position and orientation of the build platen16 or the position and orientation of the heated conduit nozzle 10 maybe controlled by a controller 20 to deposit the continuous corereinforced filament 2 in the desired location and direction as thecurrent disclosure is not limited to any particular control method.Also, any appropriate movement mechanism may be used to control eitherthe conduit or the build platen including gantry systems, robotic arms,H frames, and other appropriate movement systems. The system may alsoinclude any appropriate position and displacement sensors to monitor theposition and movement of the heated conduit nozzle relative to the buildplaten and/or a part being constructed. These sensors may thencommunicate the sensed position and movement information to thecontroller 20. The controller 20 may use the sensed X, Y, and/or Zpositions and movement information to control subsequent movements ofthe heated extrusion head or platen. For example, the system mightinclude rangefinders, displacement transducers, distance integrators,accelerometers, and/or any other sensing systems capable of detecting aposition or movement of the heated conduit nozzle relative to the buildplaten. In one particular embodiment, and as depicted in the figure, alaser range finder 15, or other appropriate sensor, is used to scan thesection ahead of the heated conduit nozzle in order to correct the Zheight of the deposition head, or fill volume required, to match adesired deposition profile. This measurement may also be used to fill invoids detected in the part. Additionally, the range finder 15, oranother range finder could be used to measure the part after thematerial is extruded to confirm the depth and position of the depositedmaterial.

Depending on the embodiment, the three dimensional printer includes acutting mechanism 8. The cutting mechanism 8 advantageously permits thecontinuous core reinforced filament to be automatically cut during theprinting process without the need for manual cutting or the formation oftails as described in more detail below. By cutting the continuous corereinforced filament during the deposition process, it is possible toform separate features and components on the structure as well ascontrol the directionality of the deposited material in multiplesections and layers which results in multiple benefits as described inmore detail below. In the depicted embodiment, the cutting mechanism 8is a cutting blade associated with a backing plate 12 located at theeyelet or outlet, though other locations are possible. While oneembodiment of the cutting mechanism including a cutting blade is shown,other types of cutting mechanisms as described in more detail below arealso possible, including, but not limited to, lasers, high-pressure air,high-pressure fluid, shearing mechanisms, or any other appropriatecutting mechanism. Further, the specific cutting mechanism may beappropriately selected for the specific feed material used in the threedimensional printer.

FIG. 1 also depicts a plurality of optional secondary print heads 18that are employed with the three dimensional printer in someembodiments. A secondary print head 18 may be used to deposit inks, orother appropriate optional coatings, on the surface of a threedimensional printed part. In one embodiment, the secondary print head issimilar to an existing inkjet printer. Such a print head may be used toprint photo-quality pictures and images on the part during themanufacturing process. The print head might use UV resistant resins forsuch a printing process. Alternatively, the print head may be used toprint protective coatings on the part. For example, the print head mightbe used to provide a UV resistant or a scratch resistant coating.

FIG. 2 presents a schematic flow diagram of a three dimensional printingprocess using the system and controller depicted in FIG. 1. Initially acontinuous core reinforced filament is provided at 102. The continuouscore reinforced filament is then fed into the heated conduit nozzle andheated to a desired temperature that is greater than a meltingtemperature of the resin and is less than a melting temperature of thecontinuous core at 104 and 106. The three dimensional printer thensenses a position and movement of the heated conduit nozzle relative tothe build platen or part at 108. After determining the position andmovement of the heated conduit nozzle, the deposition head is moved to adesired location and the continuous core reinforced filament isdeposited at the desired location and along a desired path and directionat 110. Embodiments are also envisioned in which the build platen orpart are moved relative to the deposition head. After reaching thedesired termination point, the continuous core reinforced filament iscut at 112. The controller may then determine if the three dimensionalpart is completed. If the printing process is not completed thecontroller may return to 108 during which it senses the current positionand movement of the deposition head prior to depositing the next pieceof continuous core reinforced filament. If the part is completed, thefinal part may be removed from the build platen. Alternatively, anoptional coating may be deposited on the part using a secondary printhead at 116 to provide a protective coating and/or apply a figure orimage to the final part. It should be understood that the above notedsteps may be performed in a different order than presented above.Further, in some embodiments, additional steps may be used and/oromitted as the current disclosure is not limited to only the processesdepicted in FIG. 2.

FIGS. 3A-3E depict various embodiments of core configurations of acontinuous core reinforced filaments 2. In addition to the specific coreconfigurations, the materials are processed to be substantiallyvoid-free which helps with both the binding of the individual layers andresulting strength of the final structures.

FIGS. 3A and 3B depict the cross-section of a continuous core reinforcedfilament including a solid core 6 a encased in a surrounding polymer 4or resin. There are substantially no voids present either in the polymeror between the polymer and solid core. FIG. 3A depicts a continuous corereinforced filament that includes a cross section with a largerproportion of polymer. FIG. 3B depicts a cross section with a largersolid core and correspondingly larger proportion of reinforcing corematerial. It should be understood that any appropriate proportion ofcontinuous core area to polymer area may be used. Further, materialswith a larger proportion of polymer may result in smoother surfacefinishes and better adhesion between the layers. Conversely, largerproportions of the continuous core filament may be used to increase thestrength to weight ratio of the final constructed component since thefiber material constitutes the bulk of the strength of the composite andis present in a larger proportion. A larger core may also beadvantageous when the core is made from copper or another appropriateelectrically or optically conductive material, since it may be desirableto have a large core to increase the conductivity of the depositedmaterial.

FIGS. 3C and 3D depict yet another embodiment in which the core materialof the continuous core reinforced filament 2 is a continuous multistrandcore material 6 b surrounded by and impregnated with a polymer 4 whichis wicked into the cross section of the multistrand core. FIG. 3Cdepicts a smaller proportion of multistrand core material 6 b surroundedby and impregnated with the polymer 4. FIG. 3D illustrates an embodimentwith a very small amount of resin and a large proportion of multistrandcore material 6 b such that the multistrand core material fillsvirtually the entire cross section. In such an embodiment, the polymer 4acts more as a binder impregnated into the multistrand core material 6 bto hold it together. Similar to the above noted solid cores, anyappropriate proportion of resin to multistrand core material may be usedto provide a selected strength, surface finish, conductivity, adhesion,or other desired property to the resulting continuous core reinforcedfilament 2.

FIG. 3E, depicts a variation of the continuous multistrand core. In thisembodiment, the continuous core reinforced filament 2 still includes acontinuous multistrand core material 6 b surrounded by and impregnatedwith a polymer 4. However, the core also includes one or more secondarystrands of core materials 6 c and 6 d. These secondary core materialsmight be optically conducting, electrically conducting, thermallyconducting, fluid conducting, or some combination of the above. Thesesecondary core materials could be used to conduct power, signals, heat,and fluids as well as for structural health monitoring and other desiredfunctionalities.

In order to avoid the entrapment of voids within the core reinforcedfilament 2 described above, the polymer material is processed such thatthe molten polymer or polymer resin wicks into the reinforcing fibersduring the initial production of the material. In some embodiments, thepolymer is substantially wicked into the entire cross-section of amultistrand core which helps to provide a substantially void freematerial. To produce the desired core reinforced filaments, the corereinforced filament may be pre-treated with one or more coatings toactivate the surface, and subsequently exposed to one or moreenvironmental conditions such as temperature, pressure, and/or chemicalagents such as plasticizers, to aid the polymer or resin wicking intothe cross section of the multistrand core without the formation of anyvoids. In some embodiments, this process may be performed prior toentering a feed head of the three dimensional printer. However, in otherembodiments, the core reinforced filament is formed on a completelyseparate machine prior to the printing process and is provided as aconsumable printing material. Since the subsequent deposition processdoes not need to be run at temperatures high enough to wet the corematerials with the polymer or resin, the deposition process can be runat lower temperatures and pressures than required in typical systems.While the above process may be applied to both the solid and multistrandcores, it is more beneficial to apply this process to the multistrandcores due to the difficulty associated with wicking into the multistrandcore without forming voids. Further, by forming the core reinforcedfilament either separately or prior to introduction to the depositionhead, the material width and proportions may be tightly controlledresulting in a more constant feed rate of material when it is fed into athree dimensional printer.

In contrast to the above materials formed substantially without voids,“green” deposition processes including reinforcing filaments that havebeen dipped into a resin or molten polymer and wicked with themultistrand cores during the extrusion process itself might also beused. In order to do this, the resin or polymer is heated substantiallypast the melting point, such that the viscosity is sufficiently low toallow the resin or polymer to wick into the reinforcing fibers. Thisprocess may be aided by a set of rollers which apply pressure to thematerials to aid in wicking into the reinforcing fibers. However, due tothe arrangement of the rollers and the temperature of the temperature ofthe towpreg as it exits the rollers, this process typically results invoids being entrapped in the material prior to final formation. Afterthe resin or polymer has wicked into the reinforcing fibers, theresulting “towpreg” or “tow” is typically cooled to just above themelting point prior to extrusion. However, this process is propheticallydone in air which combined with the air present in the material when itis inserted into the nozzle results in ambient air being entrapped inthe material as described in more detail below.

Such a wicking process during the extrusion of a prophetic towpreg isdepicted in FIG. 4. As depicted in the FIG. 4, prior to the wicking andextrusion process, a green towpreg 22 includes multiple green matrixresin particles or filaments 24 mixed with multiple reinforcing fibers28 as well as a surrounding amount of air 26. As depicted in the figure,the reinforcing fibers 28 are distributed randomly across the crosssection. As the towpreg 22 passes through heating zone 30 of theprophetic example of an extrusion nozzle depicted in FIG. 4, thematerial is heated to induce fiber wetting and form a cured resin 32.The surrounding air 26 also becomes entrapped in the towpreg forming airvoids 34. These entrapped air voids 34 then become embedded in theresultant printed part. Additionally, the air voids 34 may result innon-bonded sections 36 of the fibers. Since these non-bonded sections ofthe reinforcing fibers are not in contact with the polymer, theresulting composite material will be weaker in this location. Incontrast, the continuous core reinforced filament in the illustrativeembodiment depicted in FIGS. 3A-3E are substantially free from voids andin at least some embodiments the cores are centrally located within thesurrounding resin. This may result in a stronger more uniform materialand resultant part.

While the currently described three dimensional printer systems areprimarily directed to using the preimpregnated or wetted core reinforcedfilaments described herein, in some embodiments the three dimensionalprinter system might use a material similar to the green comingledtowpreg 22 depicted in the prophetic example of FIG. 4. However, asnoted above, it is desirable to avoid the formation of entrapped airvoids during curing of the material within the nozzle. One possible wayto avoid the formation of air voids in the deposited material, is toprovide a vacuum within the deposition head. By providing a vacuumwithin the deposition head, there is no air to entrap within the towpregwhen it is heated and cured within the deposition head. Therefore, insome embodiments, the deposition head is configured to allow theintroduction of a continuous green material including a solid ormultistrand core while under vacuum. The continuous green material maythen be heated to an appropriate temperature above the meltingtemperature of a resin or polymer within the continuous green materialwhile under vacuum to facilitate wicking of the resin or polymer intothe core to produce a substantially void free material. Another methodis the use of a circuitous path, which may be provided by offset rollersor other configurations as described below, to mechanically work out theentrapped air. Optionally, a vacuum may also be applied in conjunctionwith the mechanical removal of air bubbles through the circuitous path.

In addition to the material used for printing the three dimensionalpart, the specific deposition head used for depositing the corereinforced filament also has an effect on the properties of the finalpart. For example, the extrusion nozzle geometry used in typical threedimensional printers is a convergent nozzle, see FIG. 5 for a propheticexample thereof. Convergent nozzles used in typical three dimensionalprinters typically have feed stock that is about 0.060 inches to 0.120inches (1.5 mm-3 mm) in diameter. This stock is squeezed (also referredto herein as “extruded”) through a nozzle that typically necks down toabout a 0.008 inch to 0.016 inch (0.2 mm-0.4 mm) tip orifice. However,such a nozzle may not be desirable for use with feed stock including acontinuous core for the reasons described below.

As the stock material is fed into the converging nozzle, theconstraining geometry could cause the fluid polymer matrix material toaccelerate relative to a continuous core. Additionally, the matrix andcore generally have different coefficients of thermal expansion. Sincethe matrix material is a polymer it generally has a larger coefficientof thermal expansion. Therefore, as the matrix material is heated italso accelerates relative to the fiber due to the larger expansion ofthe matrix material within the confined space of the converging nozzle.The noted acceleration of the matrix material relative to the fiberresults in the matrix material flow rate Vmatrix being less than thefiber material flow rate Vfiber near the nozzle inlet. However, thematrix material flow rate at the outlet Vmatrix′ is equal to the fibermaterial flow rate Vfiber. As illustrated in the figure, thesemismatched velocities of the matrix material and fiber within theconverging nozzle may result in the fiber collecting within the nozzleduring the deposition process. This may lead to clogging as well asdifficulty in controlling the uniformity of the deposition process. Itshould be understood that while difficulties associated with aconverging nozzle have been noted above, a converging nozzle may be usedwith the embodiments described herein as the current disclosure is notlimited in this fashion.

In view of the above, it is desirable to provide a deposition headgeometry that is capable of maintaining a matched velocity of theindividual strands of multistrand core material 6 b, or otherappropriate core, and the polymer 4 or other matrix material throughoutthe deposition head for a given matrix and core combination. Forconvenience herein, deposition heads which guide a core reinforcedfilament therethrough with a matched velocity throughout are referred toas “conduit nozzles”, whereas deposition heads which neck down andextrude, under back pressure, melted non-reinforced polymer at a highervelocity than the supply filament advances are referred to as “extrusionnozzles” (according to the conventional meanings of “extrude”).

For example, FIG. 6A depicts a divergent eyelet 200 with an increasingdeposition head diameter that matches the thermal expansion of thematrix material. As depicted in the figure, the deposition head 200includes an inlet 202 with a diameter D1, a section with an increasingdiameter 204, and an outlet 206 with a diameter D2 that is greater thanthe diameter D1. By matching the deposition head diameter to theexpected expansion of the matrix material within the deposition head,the matrix and the continuous core reinforcing may be kept atsubstantially the same velocity relative to one another throughout theentire deposition head. Therefore, the linear deposition rate of thematrix material and the continuous core is the same and the continuouscore does not build up within the deposition head.

In addition to the above, in some embodiments, the matrix material andthe continuous core have relatively low coefficients of thermalexpansion (such as carbon fiber and Liquid Crystal Polymer). In such anembodiment, since the matrix material and reinforcing fibers staysubstantially the same size, the deposition head 200 may include aninlet 202 and outlet 206 that have substantially the same diameter D3,see FIG. 6B. Therefore, while some deposition head designs may havedivergent geometries, in some embodiments the deposition head geometrymay be substantially linear and may have substantially similar inlet andextrusion areas.

In addition to controlling the relative sizing of the nozzle inlet andoutlet, a deposition head 200 may also include a rounded deposition headoutlet 208, see FIG. 6C. The rounded deposition head outlet 208 may haveany appropriate form and size. For example, the rounded deposition headoutlet 208 may be embodied by an outwardly extending lip, a chamfer, afilet, an arc, or any other appropriate geometry providing a smoothtransition from the deposition head outlet. A rounded deposition headoutlet providing a smooth transition from the deposition head internalbore may help to avoid applying excessive stresses to, and/or scraping,the continuous material as it is extruded from the deposition head 200.This smooth transition provided by the rounded deposition head outletmay help to avoid fracturing the continuous core filament duringdeposition.

FIG. 7 illustrates a potential disadvantage with printing a continuouscore reinforced filament without an integrated cutter in the print head.As depicted in the figure, print head 300 is forming part 302, and isshown having deposited the last section of material layer 304. Sincetypical Fused Filament Fabrication (FFF), also known as Fused DepositionModeling (FDM), techniques place the print head close to the underlyingpart, and often touching the top of the extruded plastic, there islittle to no room in which to introduce an external cutting mechanism.Indeed, without a near zero-thickness blade, the print head needs toprint a tag-end over-run 306 not specified in the part in order toenable a separate cutting mechanism, or person, to cut the continuescore and terminate the printing process. However, this leavesundesirable tag-end over-runs 306 at each fiber termination point. Asshown in FIG. 7, a plurality of internal features, such as hard mountingbosses 308 would all have a tag-end over-run 306 at each layer withinthe boss. In view of the above, an integrated cutting mechanism mayenable less post-processing, and would allow the machine to simply printthe intended part with smaller and fewer tag-end over-runs. Further, insome embodiments, and as described in more detail below, the cuttingmechanism may eliminate the presence of tag-end over-runs altogether.

FIG. 8 depicts two embodiments of a cutting mechanism for use with athree dimensional printer. As depicted in the figure, an appropriatefeed material, which in this example is a continuous core reinforcedfilament 2 a, though other suitable filaments may be used, is removedfrom a spool 38 and passed through a feeding mechanism such as drivingroller 40 and idle wheel 42. The driving roller 40, or any otherappropriate feeding mechanism, is constructed and arranged to apply aforce directed in a downstream direction to, in this example, thecontinuous core reinforced filament 2 a. Therefore, the continuous corereinforced filament 2 a may be at a temperature such that it is in asolid or semi-solid state when this force is applied. For example, theforce may be applied to the material when it is at room temperature,below a glass transition temperature of the material, between roomtemperature in the glass transition temperature, or any otherappropriate temperature at which the material is capable of supportingthe applied force. The applied downstream force results in thecontinuous core reinforced filament 2 a entering and being extruded froma heated nozzle 10 to build up a three dimensional part. While a drivingroller has been depicted, it should be understood, that any appropriatefeeding mechanism might be used.

In the first embodiment, a cutting mechanism 8 a, such as a blade, ispositioned at the outlet of the heated conduit nozzle 10. Such aconfiguration allows actuation of the cutting mechanism to completelycut the deposited strip by severing the internal continuous core.Additionally, in some embodiments, the nozzle pressure is maintainedduring the cutting process, and the cutting blade is actuated to bothcut the internal strand, and to prevent further extrusion of thecontinuous fiber reinforced material and dripping by physically blockingthe conduit nozzle outlet. Thus, the cutting mechanism enables thedeposition of continuous core reinforced filament, as well asunreinforced materials, with precisely selected lengths as compared totraditional three dimensional printers.

In the second depicted embodiment shown integrated with the same system,a cutting mechanism 8 b is located upstream from the deposition headoutlet. More specifically, the cutting mechanism 8 b may be locatedwithin the hot end of the deposition head or further upstream before thecontinuous core reinforced filament has been heated. In someembodiments, the cutting mechanism 8 b is located between the depositionhead outlet and the feeding mechanism 40. Such an embodiment may permitthe use of a smaller gap between the deposition head outlet and the partsince the cutting mechanism does not need to be accommodated in thespace between the deposition head outlet and the part. Depending on theparticular location, the cutting mechanism 8 b may cut the continuouscore filament and the surrounding matrix while the temperature is belowthe melting or softening temperature and in some embodiments below theglass transition temperature. Cutting the continuous core reinforcedfilament while it is below the melting, softening, and/or glasstransition temperatures of the polymer may reduce the propensity of theresin to stick to the blade which may reduce machine jamming. Further,cutting when the resin or polymer is below the melting point may help toenable more precise metering of the deposited material. The position ofa cut along the continuous core reinforced filament may be selected toeliminate the presence of tag-end over-runs in the final part which mayfacilitate the formation of multiple individual features.

As shown in the figure, the downstream portion 2 b of the continuouscore reinforced filament can be severed from the upstream portion 2 a ofthe continuous core reinforced filament by the upstream cuttingmechanism 8 b. By maintaining a close fit (also referred to herein asclearance fit) between the feed material, and the guiding tube withinwhich it resides, the downstream portion 2 b of the cut strand can stillbe pushed through the machine by the upstream portion 2 a which isdriven by the drive roller 40 or any other appropriate feedingmechanism. The previously deposited and cooled material may also adhereto the previously deposited layer and will drag the continuous corereinforced filament 2 b out of the heated conduit nozzle 10 when theprint head is moved relative to the part which will apply a force to thecontinuous core located in the downstream portion of the cut strand.Therefore, a combination of upstream forces from the feeding mechanismand downstream forces transferred through the continuous core may beused to deposit the cut section of material. Again, the position of acut along the continuous core reinforced filament may be selected toeliminate the presence of tag-end over-runs in the final part.

While embodiments including an integrated cutting mechanism have beendepicted above, embodiments not including a cutting mechanism are alsopossible as the current disclosure is not limited in this fashion. Forexample embodiments in which a part is printed in a contiguous stringfashion, such that termination of the continuous material is notrequired might be used. In once such embodiment, the three dimensionalprinting machine might not be able to achieve fiber termination, andwould therefore print a length of material until the part was complete,the material ran out, or a user cuts the deposited material.

While cutting of the continuous fiber reinforced material helps toeliminate the presence of tag-end over-runs, it is also desirable toprevent buckling of the material to help ensure a uniform deposition andprevent machine jams. The stiffness of a material is proportional to thediameter of the material squared. Therefore, continuous materials withlarge diameters do not need as much support to be fed into an inlet ofthe nozzle as depicted in the figure. However, as the diameter of thecontinuous material decreases, additional features may be necessary toensure that buckling of the continuous material and any continuous corefilament contained within it does not buckle. For example, aclose-fitting guide tube as described in more detail below, may be usedin combination with positioning the feeding mechanism closer to theinlet of the nozzle or guide tube to help prevent buckling of thematerial. Therefore, in one embodiment, the feeding mechanism may belocated within less than about 20 diameters, 10 diameters, 8 diameters,6 diameters, 5 diameters, 4 diameters, 3 diameters, 2 diameters, 1diameter, or any other appropriate distance from a guide tube or inletto the deposition head.

In addition to preventing buckling, in some embodiments, the maximumtension or dragging force applied to the deposited reinforcing fibers islimited to prevent the printed part from being pulled up from acorresponding build plane or to provide a desired amount of tensioningof the continuous core. The force limiting may be provided in any numberof ways. For example, a one-way locking bearing might be used to limitthe dragging force. In such an embodiment, the drive motor may rotate adrive wheel though a one-way locking bearing such that rotating themotor drives the wheel and deposits material. If the material draggingexceeds the driven speed of the drive wheel, the one-way bearing mayslip, allowing additional material to be pulled through the feedingmechanism and nozzle, effectively increasing the feed rate to match thehead traveling speed while also limiting the driving force such that itis less than or equal to a preselected limit. The dragging force mayalso be limited using a clutch with commensurate built-in slip.Alternatively, in another embodiment, the normal force and frictioncoefficients of the drive and idler wheels may be selected to permit thecontinuous material to be pulled through the feeding mechanism above acertain dragging force. Other methods of limiting the force are alsopossible. In yet another environment, an AC induction motor, or a DCmotor switched to the “off” position (e.g. depending on the embodimentthis may correspond to either a small resistance being applied to themotor terminals or opening a motor terminals) may be used to permit thefilament to be pulled from the printer. In such an embodiment, themotors may be allowed to freewheel when a dragging force above a desiredforce threshold is applied to allow the filament to be pulled out of theprinter. In view of the above, a feeding mechanism is configured in someform or fashion such that a filament may be pulled out of the printerdeposition head when a dragging force applied to the filament is greaterthan a desired force threshold. Additionally, in some embodiments, afeeding mechanism may incorporate a sensor and controller loop toprovide feedback control of either a deposition speed, printer headspeed, and/or other appropriate control parameters based on thetensioning of the filament.

A printer system constructed to permit a filament to be pulled out of aprinter nozzle as described above, may be used in a number of ways.However, in one embodiment, the printing system drags a filament out ofa printer nozzle along straight printed sections. During such operationa printer head may be displaced at a desired rate and the depositedmaterial which is adhered to a previous layer or printing surface willapply a dragging force to the filament within the printing nozzle.Consequently, the filament will be pulled out of the printing system anddeposited onto the part. When printing along curves and/or corners, theprinting system extrudes and/or pushes the deposited filament onto apart or surface. Of course embodiments in which a filament is notdragged out of the printing system during operation and/or where afilament is dragged out of a printer head when printing a curve and/orcorner are also contemplated.

The currently described three dimensional printing methods usingcontinuous core reinforced filaments also enable the bridging of largeair gaps that previously were not able to be spanned by threedimensional printers. The deposition of tensioned continuous corereinforced filaments including a non-molten, i.e. solid, continuous coreenables the deposited material to be held by the print head on one endand adhesion to the printed part on the other end. The print head canthen traverse an open gap, without the material sagging. Thus, theprinter can print in free space which enables the printer to jump a gap,essentially printing a bridge between two points. This enables theconstruction of hollow-core components without the use of solublesupport material.

FIG. 8 depicts free-space printing enabled by the continuous corereinforced filament. With the continuous core reinforced filament 2 battached to the part at point 44, and held by the print head at point46, it is possible to bridge the gap 48. In typical FFF printers, theextruded material will sag, and fall into the gap 48 because it ismolten and unsupported. However, having a continuous core of non-moltenmaterial supporting the molten polymer enables printing in free-space,advantageously enabling many new types of printing. For example, aclosed section box shown in FIG. 9 is formed by a section 50 which isbridges gap 48 and is affixed to opposing sections 52 and 54. While thisexample shows a closed section bridge, the free-space printing couldalso be used to produce cantilevers, and unsupported beams, that cannotbe printed with typical unsupported materials.

In some embodiments, a cooling mechanism such as a jet of cooling airmay be applied to the extruded material to further prevent sagging bysolidifying the polymer material surrounding the core. The extrudedmaterial may either be continuously cooled while building a componentwith sections over gaps. Alternatively, in some embodiments, theextruded material might only be cooled while it is being extruded over agap. Selectively cooling material only while it is over a gap may leadto better adhesion with previously deposited layers of material sincethe deposited material is at an elevated temperature for a longer periodwhich enhances diffusion and bonding between the adjacent layers.

In the above noted embodiments, a cutting blade is located upstream ofthe nozzle to selectively sever a continuous core when required by aprinter. While that method is effective, there is a chance that afilament will not “jump the gap” correctly between the cutting mechanismand the nozzle. Consequently, in at least some embodiments, it isdesirable to increase the reliability of rethreading the core materialafter the cutting step.

As described in more detail below, in some embodiments, a cuttingmechanism is designed to reduce or eliminate the unsupported gap afterthe cutting operation. In such an embodiment, a tube-shaped shear cuttermay be used. As described in more detail below, a core reinforcedfilament is contained within two intersecting tubes that shear relativeto each other to cut the core reinforced filament. In such anembodiment, a gap sufficient to accommodate movement of the two tiltedto each other. The tubes are subsequently moved back into alignment toresume feeding the material. In this mechanism there is effectively nogap to jump after the cutting operation since the tubes are realignedafter cutting. In some embodiments, the gap required for the cuttingoperation is reduced or eliminated by moving the guide tubes axiallytogether after the cut, thus, eliminating the gap and preventing thefiber from having to jump the gap. In other embodiments, and asdescribed in more detail below, the cutting mechanism may be integratedinto a tip of a printer deposition head to eliminate the need for a gap.

FIG. 10 depicts a compression-based continuous-core print head. Asdepicted in the figures, the input material comprises a towpreg such asa continuous core filament 2 which is drawn into the feed rollers 40 and42 under tension. To facilitate guiding and maintaining alignment of thecontinuous core filament 2 with the rollers 40 and 42, in someembodiments, the continuous core filament 2 passes through a guide tube74 positioned upstream of the rollers. After passing through therollers, the continuous core filament 2 is placed in compression. Asnoted above, depending on a length of the material under compression aswell as a magnitude of the applied force, the continuous core filament 2may tend to buckle. Consequently, in some embodiments, the continuouscore filament 2 passes through a close-fitting guide tube 72 positioneddownstream of the rollers and upstream of the nozzle. The guide tube 72will both guide and substantially prevent buckling of the continuouscore filament 2. Similar to the above embodiments, a cutting mechanism 8corresponding to a blade is positioned downstream of the guide tube 72.The gap 62 present between the conduit printer head 70 and the cuttingmechanism 8 is illustrated in the figure. When the continuous corefilament 2 is cut by the cutting mechanism 8, the material is“rethreaded” by passing from one side of the gap 62 to the other sideand into receiving tube 64. In some embodiments, the receiving tube 64is advantageously below the glass transition temperature of thematerial, such that the entirety of the cutting operation occurs withinsolid material. In the depicted embodiment, a thermal spacer 66 islocated between the receiving tube 64 and the hot melt conduit nozzle68. The thermal spacer 66 reduces the heat transfer to the receivingtube 64 from the hot melting conduit nozzle 68. Similar to the previousembodiment, the continuous-core material 2 is deposited, layer-by-layer14 onto a build plate 16. FIG. 11 is a photograph of a system includingthe above-noted components.

In some embodiments, the filament used with the device depicted in FIG.10 is provided on a spool 76. When provided in this form, the materialis preformed, substantially solid, and substantially rigid. For example,a preimpregnated core reinforced filament might be provided. Since thematerial has already been formed, it is less likely to stick to thevarious components and/or delaminate during use as might be the case fora green towpreg which may or may not include an uncured resin. Byproviding the filament in a preformed state, the filament is able tosupport compressive forces in addition to being easier to manipulate.This facilitates both handling during threading of the system as well asapplying compressive forces to the material during deposition using acompression-based printer head as described herein.

The difficulty in jumping the gap 62 depicted in FIG. 10 stems from afew key areas. The first difficulty in rethreading is due to the factthat the filament is inherently more flexible during threading when theend is unsupported, than after it has been threaded and both ends arefully supported and constrained. More specifically, the bending mode issecond order when rethreaded, which is inherently stiffer, and lessprone to bending or buckling, than a filament constrained only at theupstream end corresponding to a first order bending mode. Additionally,after the filament has been threaded, the downstream portion serves toguide all the subsequent flowing material into the tube. Finally,cutting a filament introduces deformation to the feed material which mayresult in misalignment of the filament and the receiving tube 64. Thismisalignment may result in the filament not appropriately feeding intothe receiving tube 64 after cutting. This deformation can be minimizedthrough the use of stiff matrix material, and a sharp cutting blade.However, blade wear, and the desire to use different types of materials,means that in some applications it may be desirable to use a differentcutting mechanism or additional features to increase threadingreliability.

There are several ways to improve the reliability of threading thefilament past a cutting mechanism. For example, in one embodiment, thegap 62 is selectively increased or decreased to permit the introductionof the blade. In such an embodiment, when not in use, the cuttingmechanism 8 is removed from the gap 62 and the guide tube 72 isdisplaced towards the receiving tube 64. This reduces, and in someembodiments, eliminates the gap 62 during rethreading. Alternatively,the guide tube 72 may be constructed and arranged to telescope, suchthat a portion of the guide tube moves towards the receiving tube 64while another portion of the guide tube stays fixed in place to reducethe gap. In another embodiment, rethreading error is reduced using aflow of pressurized fluid, such as air, that is directed axially downthe guide tube 72. The pressurized fluid exits the guide tube 72 at thecutting mechanism 8 as depicted in the figure. As the continuous corefilament 2, or other appropriate material, is advanced through gap 62,the axial fluid flow will center the material within the fluid flow thusaiding to align the material with the receiving end 16. Such anembodiment may also advantageously serve to cool the guide tube 72 tubeduring use. This may help facilitate high-speed printing and/or higherprinting temperatures. The fluid flow may also help to reduce frictionof the material through the guide tube.

FIG. 12A depicts one embodiment of a shear cutting mechanism. The shearcutting mechanism also eliminates the gap 62 of FIG. 10 which willincrease the reliability of threading. Similar to the above, thecontinuous filament 400 is driven in compression by drive wheel 408, andreceived by a close-fitting guide tube 420. The material is driven incompression through an upper shear cutting block guide 406, lower shearcutting head 402, and heated print head 404. The upper shear cuttingblock 406 and lower shear cutting head 402 are displaced relative toeach other to apply a shearing force to the filament to cut it. While aparticular mechanism has been depicted in the figures, it should beunderstood that any configuration capable of providing a shearing forceto the material might be used. For example, first and second shearingelements may include aligned channels that are shaped and size to accepta filament. The first and/or second shearing elements may then bedisplaced relative to one another to take the channels formed in thefirst and second shearing elements out of alignment and apply a shearforce to the filament to cut it. Additionally, the shear cuttingmechanism may located within a print head, or upstream of the printhead, as the disclosure is not so limited.

FIG. 12B shows the upper shear cutting block 406 translated relative toshear cutting head 402. As noted above, when the upper shear cuttingblock is translated relative to the shear cutting head, the filamentsegment 422 is sheared off from the continuous filament 400. If a simplecut is desired, the shear head 402 can return to the original positionrelative to the upper cutting block 406. In the presented diagram, theupper block moves. However, either block, or both blocks, could movedepending on the particular design. The shear cut and return action isthe simplest cutting formation. After the shear cut and return, the endof the filament 400 is entirely captive in the guiding tube. Therefore,there is no gap to jump, thus, increasing the reliability of feeding thefilament forward for the next section of the part.

In addition to simply performing sheer cutting of a material, in someembodiments, it may be desirable to provide printing capabilities withmultiple types of materials and/or operations. FIG. 12A illustrates oneembodiment of a system including optional indexing stations 414 and 416.When shear head 402 is translated over to either station, a plurality ofuseful operations can additionally occur. In one embodiment, station 416is a cleaning station and includes a cleaning material 410, that can befed through the print head 404 to clean the nozzle. In one example, thematerial is a metal like brass, copper, stainless steel, aluminum, orthe like. This enables the nozzle to be heated, and purged with amaterial having a higher melting temperature than the feed stock. In oneembodiment, the print head 404 is moved to a print cleaning station, forexample, the back corner or other appropriate location. The print head404 is then heated up and indexed to station 416. The cleaning material410 is then fed through the nozzle to clear any obstructions present.The shear cutting action of the upper sheer cutting block 406 and thelower shear cutting head 402 can then sever the sacrificial cleaningpieces to prevent them from being dragged back up the nozzle, andthereby introducing contaminants to the nozzle. In some instances,however, the cleaning agent may be cyclically pushed down, and pulledback up through the nozzle. In another embodiment, the cleaning station416 is used to push any number of cleaning agents such as high-pressureair, liquids, solids, gasses, plasmas, solvents or the like, through thenozzle in order to perform the desired cleaning function.

In addition to the above, in some embodiments, the three-dimensionalprinting system also includes a station 414 corresponding to a differentmaterial 412. Depending on the particular application, the secondmaterial may be an electrically conductive material such as copper, anoptically conductive material such as fiber optics, a second corereinforced filament, plastics, ceramics, metals, fluid treating agents,solder, solder paste, epoxies, or any other desired material as thedisclosure is not so limited. In such an embodiment, the printdeposition head 404 is indexed from one of the other stations to thestation 414 to deposit the second material 412. When the printingfunction using the second material is finished, the print depositionhead 404 is then indexed from station 414 to the desired station andcorresponding material.

FIG. 13 shows a shear cutting block 402 including multiple depositionheads 404 and 424 formed in the shear cutting block. In one embodiment,the deposition head 404 has a larger print orifice than the depositionhead 424, enabling larger diameter towpregs and/or pure polymermaterials to be deposited at a more rapid volume. In another embodiment,the second deposition head 424 is substantially the same as depositionhead 404. Consequently, the second deposition head 424 may be used as areplacement nozzle that can be automatically switched into use ifdeposition head 404 becomes clogged. Having an additional nozzle woulddecrease the down time of the machine, especially in unattended printing(e.g. overnight). Similar to the above, the first and second depositionheads 404 and 424 may be indexed between different stations.

FIG. 14A depicts a nozzle 500 including an inlet 502 and an outlet 504.The geometry of the deposition head outlet 504 includes a sharp exitcorner. While some embodiments may use a nozzle with a sharp corner atthe outlet, a sharp corner may lead to cutting of fibers in continuouscore printing. Further, it may scrape off plating of metal cores, andtreatments applied to fiber optic cables incorporated in a core.Consequently, in some embodiments, it is desirable to provide a smoothtransition at an outlet of a nozzle. FIG. 14B depicts a chamfered nozzleoutlet 506, which reduced shear cutting of fibers in testing. Smoothlyrounded nozzle exit 508 advantageously reduces shearing and cutting ofnon-molten continuous cores. It should be appreciated that theparticular design of a transition at an outlet of a nozzle includesaspects such as chamfer angle, fillet angle and degree, length of thetransition, and other appropriate considerations that will varydepending on the particular material being used. For example, Kevlar isextremely strong in abrasion, while fiberglass is weak. Therefore, whilea nozzle including a 45 degree chamfer may be sufficient for Kevlar, itmay result in broken strands when used with fiber glass. However, byusing additional chamfers, or other features, it is possible toeliminate breakage of the fiberglass cores during printing.

As depicted in the figures, deposition head outlet geometries 506 and508 provide a smooth transition from the vertical to the horizontalplane to avoid accidently cutting the core materials. However, in someembodiments, it may be desirable to sever the continuous core to cut thefilament. One method of severing the continuous core at the tip of thenozzle 500 is to push the nozzle down in the vertical Z direction, asshown by arrow 210. As depicted in FIG. 14C, in some embodiments, thecorner of the deposition head outlet 508 is sharpened and oriented inthe Z direction to enable the outlet to sever the continuous core as theoutlet impinges on and cuts through the material. In order to facilitatecutting of the material using such a method, it may be desirable toplace the material under tension. This tension may be provided in anynumber of ways including, for example, providing a firm hold of thematerial using the feeding mechanism, reversing the feeding mechanismand/or moving the print head. Alternatively, the nozzle 500 might bekept stationary while the feeding mechanism is reversed in order to pullthe material against the edge of the deposition head outlet and cut it.In another embodiment, the cutting can be achieved by simply “breaking”the strand at the corner point where it exits the deposition head byadvancing the deposition head, without feeding, thereby building tensionuntil the core is severed. Typically this will occur at the corner pointof the nozzle exit. In this embodiment, a compromise nozzle design maybe selected. The nozzle exit geometry may be slightly sharpened in orderto enhance cutting.

In another embodiment, a portion of a nozzle may be sharpened anddirected towards an interior of the conduit nozzle eyelet or outlet toaid in cutting material output through the nozzle. As depicted in FIGS.15A-15D, a nozzle 600 contains a continuous core filament 2, or otherappropriate material, exiting from a chamfer style deposition head. Asdepicted in the figures the nozzle 600 is smoothly chamfered.Additionally, the nozzle 600 includes a ring 602 located at a distaloutlet of the nozzle. The majority of the ring 602 is a non-cuttingportion of the ring and is shaped and arranged such that it does notinterfere with material being output from the nozzle. However, the ring602 also includes a cutting portion 602 a which is sharpened andoriented inwards towards the material contained within the nozzle 600,see FIGS. 15B-15D. Depending on the particular embodiment, the cuttingportion 602 a is a sharp cutting blade. The cutting portion may be madeof a cutting steel, a stainless steel, a carbide, a ceramic, or anyappropriate material. As illustrated in FIG. 15D, in some embodiments,the cutting portion 602 a occupies a fraction of the conduit nozzleeyelet or outlet area. In such an embodiment, the cutting portion 602 amay either be permanently attached in the indicated position within theconduit nozzle eyelet or outlet, or it may be selectively retractedduring the printing process and deployed into a cutting position when itis desired to cut the printed material as the disclosure is not solimited. Alternatively, in other embodiments, the cutting portion 602 ais recessed into a perimeter of the conduit nozzle eyelet or outlet suchthat it does not impinge upon material exiting the nozzle during normaloperation. For example, the cutting portion 602 a may form a part of theperimeter of the nozzle exit as depicted in FIG. 15C. Other arrangementsof the cutting portion 602 a relative to the conduit nozzle eyelet oroutlet are also contemplated. Additionally, while the cutting portion602 a has been depicted as being incorporated with a ring attached to anozzle, embodiments in which the cutting portion is either formed withthe conduit nozzle eyelet or outlet and or directly attached to theconduit nozzle eyelet or outlet are also contemplated.

With regards to the embodiment shown in FIGS. 15A-15D, when it isdesired to cut material being extruded from the nozzle, such as, forexample, the continuous core filament 2, the nozzle is translated in adirection D relative to a part being constructed on a surface, see thearrows depicted in the figures. During this translation, the continuouscore filament 2 is not fed through the nozzle. Consequently, thecontinuous core filament 2, and the core contained within it, iseffectively held in place. This results in the tensioning of the corematerial 6 which is displaced towards the cutting portion 602 a throughthe surrounding polymer matrix 4. As increasing tension is applied tothe continuous core filament 2, the core 6 is cut through by the cuttingportion 602 a. Alternatively, in some embodiments, the surface and/orpart is translated relative to the nozzle as the disclosure, or thecontinuous core filament 2 is retracted using the feeding mechanism toapply the desired tension to the core material 6 to perform the severingaction.

While a solid core with a particular size has been depicted in thefigures, it should be understood that the disclosure is not so limited.Instead, such a cutting mechanism may be used with solid cores,multi-filament cores, continuous cores, semi-continuous cores, purepolymers, or any other desired material. Additionally, the core material6 may be any appropriate size such that it corresponds to either alarger or smaller proportion of the material depicted in the figures. Inaddition to the above, for some materials, such as fiber optic cables,the cutting portion 602 a forms a small score in the side the core 6,and additional translation of the nozzle relative to the part completesthe cut. For other materials, such as composite fibers, the roundedgeometry of the nozzle results in the core 6 being directed towards thecutting portion 602 a when it is placed under tension as describedabove. Therefore, the resulting consolidation (e.g. compaction) of thecore towards the cutting portion enables cutting of a large fiber with arelatively smaller section blade. In yet another embodiment, the core 6is either a solid metallic core or includes multiple metallic strands.For example, the core may be made from copper. In such an embodiment,the cutting portion 106 a creates enough of a weak point in the materialthat sufficient tensioning of the core breaks the core strand at thenozzle exit. Again, tensioning of the core may be accomplished throughnozzle translation relative to the part, backdriving of the material, ora combination thereof.

In yet another embodiment, the cutting portion 602 a is a hightemperature heating element that heats the core in order to sever it,which in some applications is referred to as a hot knife. For example,the heating element might heat the core to a melting temperature,carbonization temperature, or to a temperature where the tensilestrength of the core is low enough that it may be broken with sufficienttensioning. It should be understood that, the heating element may heatthe core either directly or indirectly. Additionally, in someembodiments, the element is a high-bandwidth heater, such that it heatsquickly, severs the core, and cools down quickly without impartingdeleterious heat to the printed part. In one particular embodiment, theheating element is an inductive heating element that operates at anappropriate frequency capable of heating the core and/or the surroundingmaterial. In such an embodiment, the inductive heater heats the core toa desired temperature to severe it. Such an embodiment may be used witha number of different materials. However, in one embodiment, aninductive heater is used with a continuous core filament including ametallic core such as copper. The inductive heating element heats themetallic core directly in order to severe the strand. In instances wherethe heating element indirectly heats the core, it may not be necessaryto tension the material prior to severing the core. Instead, the coremay be severed and the nozzle subsequently translated to break thematerial off at the conduit nozzle eyelet or outlet.

FIG. 16 presents another embodiment of a nozzle tip-based cuttingmechanism in the depicted embodiment, a cutting element 604 is disposedon a distal end of the nozzle 600. While any appropriate arrangementmight be used, in the depicted embodiment a cutting ring disposed aroundthe distal end of the nozzle as depicted in the figure. The cutting ring604 includes a sharp and edge oriented towards the deposited continuouscore filament 2 depicted in the figure. In such an embodiment, thecutting element 604, or a subsection thereof, is actuated downwardstowards the deposited material in order to sever the core of thecontinuous core filament 2. In another version, the internal nozzle 600is translated upwards relative to the cutting element 604. In such anembodiment, the conduit nozzle 600 may be spring loaded down. Therefore,a cut can be executed by driving the feed head into the part, therebydepressing the inner feed head, relative to the cutting ring, andenabling the cutting ring to sever the core material. In either case,the continuous core filament 2 is brought into contact with the cuttingelement 604, and the core material 6 is severed.

While several different types of cutting mechanisms are described above,it should be understood that any appropriate cutting mechanism capablesevering the core and/or surrounding matrix might be used. Therefore,the disclosure should not be limited to just the cutting mechanismsdescribed here core the particular core material and structure describedin these embodiments.

As noted above, tension-based three-dimensional printing systems couldexhibit several limitations, including the inability to make planar orconvex shapes as well as difficulty associated with threading theprinted material through the system initially and after individual cuts.In contrast, a compression-based three-dimensional printing systemoffers multiple benefits including the ability to make planar and convexshapes as well as improved threading of the material. However, as notedpreviously, in some modes of operation, and/or in some embodiments,material may be deposited under tension by a system as the disclosure isnot so limited.

Referring again to FIG. 10, a three-dimensional printing system mayinclude a feeding mechanism such as a roller 40 capable of applying acompressive force to the continuous core filament 2 fed into a printerhead 70. However, as noted above, extruding a towpreg, strand, fiber, orother similar material using a compressive force may result in buckling.Consequently, it is desirable to prevent buckling of the material whenit is under compression. Composite fibers are incredibly stiff whenconstrained in place such as when they are held in place by a matrix.However, composite fibers are easily flexed when dry in a preimpregnatedform when they are not constrained from moving in off axis directions.Therefore in some embodiments, it is desirable to constrain movement ofthe material in off axis directions. While this may be accomplished in anumber of ways, in one embodiment, and as noted above, one or more closefitting guide tubes 72 are located between the feeding mechanism and thereceiving tube 64 or other inlet of the nozzle. The one or more closefitting guide tubes 72 located along the fiber length help to preventbuckling. The distance between the feeding mechanism, such as the roller40, and an inlet of the guide tube 72 may be selected to substantiallyavoid buckling of the material as well. In some embodiments, it isdesirable that the guide tubes are close fitting and smooth such thattheir shape and size are substantially matched to the continuous corefilament 2. In one specific embodiment, the guide tube is a roundhypodermic tube. However, embodiments in which the guide tube is sizedand shaped to accept an ovular, square, tape-like material, or any otherappropriately shaped material are also contemplated. In someembodiments, and as described in more detail below, the continuous corefilament 2 may include a smooth outer coating and/or surface, which isin contrast to tension wound systems where the core may poke through theouter jacket. This smooth outer surface may advantageously reduce thefriction the material within the close fitting guide tubes.

In some embodiments, the three-dimensional printing system does notinclude a guide tube. Instead, the feeding mechanism may be locatedclose enough to an inlet of the nozzle, such as the receiving tube 64,such that a length of the continuous core filament 2 from the feedingmechanism to an inlet of the nozzle is sufficiently small to avoidbuckling. In such an embodiment, it may be desirable to limit a forceapplied by the feeding mechanism to a threshold below an expectedbuckling force or pressure of the continuous core filament, or othermaterial fed into the nozzle.

In addition to depositing material using compression, the currentlydescribed three dimensional printers may also be used with compactionpressure to enhance final part properties. For example, FIG. 17A shows acomposite material, such as the continuous core reinforced filament 2,that is ironed through a printer head 60 with an applied compactionforce or pressure 62. The compaction pressure compresses the initialcontinuous core reinforced filament 2 a with an initial shape, see FIG.17B, into the preceding layer below and into a second compacted shape,see FIG. 17C. The compressed continuous core reinforced filament 2 bboth spreads into adjacent strands 2 c on the same layer and iscompressed into the underlying strands of material 2 d. This type ofcompaction is typically achieved in composites through pressure plates,or a vacuum bagging step, and reduces the distance between reinforcingfibers, and increases the strength of the resultant part. While theprinter head 70 may be used to apply a compression pressure directly tothe deposited material other methods of compressing the depositedmaterials are possible. For example the deposited materials might becompacted using: pressure applied through a trailing pressure platebehind the head; a full width pressure plate spanning the entire partthat applies compaction pressure to an entire layer at a time; and/orheat may be applied to reflow the resin in the layer and achieve thedesired amount of compaction within the final part.

As noted above, and referring to FIG. 18A, nozzles 700 used in FusedFilament Fabrication (FFF) three dimensional printers typically employ aconstriction at the tip of the nozzle to trap the solid, non-moltenplastic when it first enters the nozzle at inlet 702 and passes into theheated block 704. The converging nozzle outlet 706 appliesback-pressure, or retarding force, that only enables material to passthrough the nozzle once it has melted, and can squeeze through thesignificantly smaller diameter outlet 706. One of the problemsassociated with Fused Filament Fabrication is the eventual clogging andjamming of the print head (nozzle) due to the convergent nozzle designtrapping material with no means of ejecting it. Further, degradedplastic builds up within the nozzle which eventually clogs the nozzle oralters the extruded print bead. Additionally, in order to clean aconvergent nozzle, the feeding filament must be reversed backwards upthrough the nozzle, potentially contaminating the feed path back to thefilament spool. After reversing through the entire feed path, thecontaminated tip of the feed material must be cut off from the feedspool, and the spool must be re-threaded through the machine. For thesereasons, the nozzles on most FFF three-dimensional printers areconsidered wear items that are replaced at regular intervals.

Having realized these limitations associated with convergent nozzles,the inventors have recognized the benefits associated with a divergentnozzle. In a divergent nozzle, the inflowing material expands as ittransitions from the feed zone, to the heated melt zone, therebyenabling any particulate matter that has entered the feed zone to beejected from the larger heated zone. Additionally, a divergent nozzle isboth easier to clean and may permit material to be removed and a feedforward manner where material is removed through the nozzle outlet ascompared to withdrawing it through the entire nozzle as described inmore detail below.

FIG. 18B shows a nozzle 708 including a material inlet 710, fluidlyconnected to cold-feed zone 712. In the depicted embodiment, the inlet710 and the cold feed zone 712 correspond to a cavity or channel with afirst size and shape. The cold feed zone 712 is disposed on top of himfluidly connected to a heated zone 714. A cross-sectional area of thecavity or channel depicted in the heated zone 714 that is transverse toa path of the filament when positioned therein is greater than across-sectional area of the cavity or channel located in the cold-feedzone 712 that is transverse to the path of the filament. Additionally,in some embodiments, a cross-sectional area of the nozzle outlettransverse to the path of the filament is greater than a cross-sectionalarea of the nozzle inlet transverse to the path of the filament. Thenozzle also includes a nozzle outlet 716. During use, material passesfrom the nozzle inlet 710, through the cold feed zone 712, and into theheated zone 714. The material is then output through the nozzle outlet716. In some embodiments, the cold-feed zone 712 is constructed of amaterial that is less thermally conductive than a material of the heatedzone 714. This may permit the material to pass through the cold feedzone 712 and into the heated zone 714 without softening. In oneparticular embodiment, a divergent nozzle is formed by using alow-friction feeding tube, such as polytetrafluoroethylene, that is fedinto a larger diameter heated zone located within a nozzle such that aportion of the heated zone is uncovered downstream from the tube.Additionally, depending on the embodiment, one or both of the coolfeeding zone and heating zone may be constructed from, or coated with, alow friction material such as polytetrafluoroethylene. While a sharptransition between the cold feed zone and the heated zone has beendepicted in the figures, embodiments of a divergent nozzle in whichthere is a gradual transition from a smaller inlet to a larger outletare also contemplated.

One of the common failure modes of FFF is the eventual creep up of themolten zone into the cold feeding zone, called “plugging”. When the meltzone goes too high into the feed zone, and then cools during printing,the head jams. Having a divergent nozzle greatly reduces the likelihoodof jamming, by enabling molten plastic to be carried from a smallerchannel, into a larger cavity of the divergent nozzle. Additionally, asdescribed below, a divergent nozzle is also easier to clean.

FIG. 18C depicts an instance where a divergent nozzle 708 has beenobstructed by a plug 718 that has formed within the heated zone 714 andbeen removed. Advantageously, a divergent nozzle can be cleaned using aforward-feeding cleaning cycle. In one embodiment, a forward feedingcleaning cycle starts by extruding a portion of plastic onto a print bedsuch that the plastic adheres to the print bed. Alternatively, thesystem may deposit the material onto a cleaning area located at a backof the printing system away from the normal build platform or on anyother appropriate surface as the disclosure is not so limited. Afterattaching to the surface, the system is cooled down to permit thematerial located within the heated zone 714 to cool below the meltingtemperature of the material. After solidification, the print bed andnozzle are moved relative to each other to extract the plug 718 from thenozzle 708. For example, the print bed might be moved down in the zdirection. Alternatively, a printer head including the nozzle might bemoved in a vertical z direction away from the print bed. Additionally,in some embodiments, a feeding mechanism associated with the feedmaterial is driven to apply an additional force to the material as theplug is pulled out of the nozzle. Either way, the plug is then pulledout of the nozzle, advantageously removing debris previously stuck tothe wall, and is done without having to retract the feed material fromthe nozzle through the feed path. While any appropriate material may beused with a divergent nozzle, in some embodiments, a divergent nozzle isused with a material including nylon. This may be beneficial because thecoefficient of thermal expansion for nylon causes it to pull away fromthe nozzle slightly during cooling and nylons exhibit low coefficient offriction. Again, the use of polytetrafluoroethylene within one, or bothof the cold feed zone and the heated zone, may help facilitate the easyremoval of plugs formed within the nozzle.

While a method of use in which the divergent nozzle is cleaned byattaching a plug to a surface, in another embodiment, a cleaning cycleis performed by simply extruding a section of plastic into free air. Theplastic may then be permitted to cool prior to being removed by hand orusing an automated process. When the material is removed, any plugattached to that material is also removed.

In another embodiment, a forward feeding cleaning cycle is used with aslightly convergent nozzle. For example, convergent nozzles with anoutlet to inlet ratio of 60% or more might be used, though other outletto inlet ratios are also possible. The forward extrusion cleaning methodfor such a nozzle includes extruding a section of molten material, andoptionally attaching it to the print bed. The heated nozzle is thenallowed to cool. During the cooling process, the ejected portion ofmaterial is pulled such that the material located within the heated zoneis stretched, thereby reducing a diameter of the material. The materialmay be stretched to a degree such that the diameter of the materiallocated within the heated zone is less than a diameter of the nozzleoutlet. Additionally, once the material has cooled, further pullingenables diameter contraction through the Poisson's ratio of thematerial, thereby further facilitating removal of the remnant locatedwithin the nozzle. In some embodiments, the material is stretched byapplying a force by hand, or other external means, to the extrudedmaterial. In other embodiments where the material is attached to asurface, the printer head and/or surface are displaced relative to eachother as noted above to apply a force to the material to provide thedesired structure. The above described method enables the feed forwardcleaning of a slightly convergent nozzle to be cleaned with forwardmaterial flow.

While a divergent nozzle has been discussed above, embodiments in whicha straight nozzle is used for FFF printing are also contemplated. FIG.19A depicts a nozzle 720 including an inlet 724 that is substantiallythe same size as nozzle outlet 722. A material such as a continuous corefilament 2 passes through a cold feed zone 712 and into a heated zone714. In one embodiment, the cold feed zone is a low friction cold-feedzone made from a material with a low coefficient of thermal conductionsuch as polytetrafluoroethylene. Correspondingly, the heated zone 714 ismade from a more thermally conductive material such as copper, stainlesssteel, brass, or the like. Regardless of the specific construction,after melting, the continuous core filament 2 is deposited on, andattached to, a build platen 16 or other appropriate surface. Straightnozzles are ideally suited to small diameter filaments, on the order ofabout 0.001″ up to 0.2″. However, embodiments in which materials withdiameters both greater than and less than those noted above are usedwith a substantially straight nozzle are also contemplated. The lowthermal mass associated with these small filaments permits them to heatup quickly. Additionally, the small dimensions permit these materials tobe extruded at substantially the same size as they are fed into theprint head. Similar to a divergent nozzle, a substantially straightnozzle offers the advantages of forward feeding cleaning cycles thatenables a cooled plug to be removed from the tip and substantiallyavoiding collecting particles and debris within the nozzle.

A nozzle similar to that described in FIG. 19A can also be used with atypical green towpreg 734. However, this may result in clogging similarto prophetic three dimensional printing systems using a green towpreg.The clogging is a result of trying to “push” a flexible composite strandthrough a nozzle in the initial stitching operation. FIG. 19Billustrates would happen when a green towpreg is output through nozzle720 during an initial stitching operation to attach it to a part orbuild plate. Namely, instead of being pushed through the nozzle asintended, the individual fibers in the green towpreg 734 would tend tostick to the walls of the nozzle and commensurately start to bend andcurl up at 736. Put another way, the flexible fibers located within agreen or flexible towpreg are likely to delaminate and become clogged inthe nozzle. Flexible materials may include, but are not limited to, amolten thermoplastic and/or un-cured plastic for two part mixed epoxy orlaser cured resins, though other flexible materials are also possible.

In contrast to the above, a stitching process associated with apreimpregnated continuous core filament within a divergent nozzle doesnot suffer the same limitations. More specifically, FIGS. 19C-19Eillustrate a method of stitching using a rigid preimpregnated continuouscore filament fed through a divergent nozzle, such that clogging isreduced, or substantially eliminated. FIG. 19C shows a continuous corefilament 2 located within the cold feed zone 712. Depending on theparticular embodiment, the material may be located on the order of 5inches or more from the heated zone 714, though other distances are alsocontemplated. Additionally, in embodiments where the material has alarger thermal capacity and/or stiffness, it may be located closer tothe heated zone 714 to provide pre-heating of the material prior tostitching. While located within the cold feed zone 712, which is below amelting temperature of the matrix, the continuous core filament 2remains substantially solid and rigid. The continuous core filament 2 ismaintained in this position until just prior to, printing. At thatpoint, the continuous core filament 2 is quickly stitched through theconduit nozzle, i.e. displaced through the conduit nozzle eyelet oroutlet, see FIG. 19D. Since the cold-feed zone 712 feeds into a largercavity corresponding to the heated zone 714, when the material isstitched, the continuous core filament 2 is constrained from touchingthe walls of the heated zone 714 by the portion of the filament stilllocated in the outlet of the cold feed zone, see FIG. 19D. By performingthe stitching quickly, melting of the matrix may be minimized tomaintain a stiffness of the composite material. By maintaining astiffness of the material and preventing melting until the material hasbeen stitched, it is possible to prevent fibers from peeling off,curling and/or clogging within the nozzle. This may enable the feedmaterial to be more easily pushed into, and through, the hot-melt zone.In some embodiments, a blast of compressed air may be shot through thenozzle prior to and/or during stitching in order to cool the nozzle toreduce the chance of sticking to the sides of the nozzle. Additionally,heating of the heated zone 714 of the nozzle may be reduced oreliminated during a stitching process to also reduce the chance ofsticking to the sides of the nozzle.

As feeding of the continuous core filament 2 continues, the continuouscore filament 2 eventually contacts the build platen 16, or otherappropriate surface. The continuous core filament 2 is then draggedacross the surface by motion of the nozzle relative to the build platen16. This results in the continuous core filament 2 contacting the wallsof the heated zone 714 as illustrated in FIGS. 19E and 20A at or nearthe lip 726. Alternatively, instead of translating the printer head, thematerial could be driven to a length longer than a length of the nozzle.When the outlet of the nozzle is blocked by a previous layer of thepart, or by the print bed, the material will buckle and contact thewalls of the heated zone 714 as illustrated in FIGS. 19E and 20A at ornear the lip 726. Regardless of the particular method employed, aftercontacting the walls of the heated zone 714 as illustrated in FIGS. 19Eand 20A at or near the lip 726, the continuous core filament 2 is heatedup to a desired deposition temperature capable of fusing the depositedmaterial to a desired surface and/or underlying previously depositedlayers thus enabling three-dimensional printing. For example, oncetranslation of the print head begins, the matrix material contacts awall of the heated zone as illustrated in FIGS. 19E and 20A at or nearthe lip 726 and is heated to a melting temperature of the matrixmaterial. Stitching speeds obtained with a system operated in the mannerdescribed above, was capable of stitching speeds between about 2500mm/min and 5000 mm/min. However, the stitching speed will vary based onnozzle heating, matrix material, and other appropriate designconsiderations. While a particular stitching method has been describedabove, it should be noted that other types of stitching and meltingtechniques could also be employed as the disclosure is not limited toany particular technique.

As also depicted in FIGS. 19C-19E, in some embodiments, the nozzle 708may include a rounded or chamfered lip 726, or other structure, locatedat a distal end of the conduit nozzle eyelet or outlet 716. This mayserve two purposes. First, as noted previously, a gradual transition atthe conduit nozzle eyelet or outlet may help to avoid fracturing of thecontinuous core. Additionally, in some embodiments, the lip 726 ispositioned such that the lip applies a downward force to the continuouscore filament 2 as it is deposited. This may in effect applying acompaction force to the material as it is deposited which may “iron” thecontinuous core filament down to the previous layer (as illustrated inFIGS. 19E and 20A at or near the lip 726). As noted above compactionforces applied to the material may offer multiple benefits includingincreased strength and reduced void space to name a few. This compactionforce may be provided by positioning the lip 726 at a distance relativeto a deposition surface that is less than a diameter of the continuouscore filament 2. However, compaction forces provided using distancesgreater than a diameter of the continuous core filament are alsopossible for sufficiently stiff materials. This distance may beconfirmed using an appropriate sensor, such as a range finder, as notedabove. In some embodiments, the lip 726 is incorporated with asubstantially straight nozzle 720 or a slightly convergent nozzle as thedisclosure is not so limited, see FIG. 20A.

While the above embodiments have been directed to divergent and straightconduit nozzles including a cold feed zone and a separate heated zone,embodiments in which a convergent conduit nozzle eyelet includes aseparate cold feed zone and heated zone are also contemplated. Forexample, FIG. 20B shows an conduit nozzle eyelet 728 including a conduitnozzle eyelet inlet 730 that feeds into a cold feed zone 712 which is influid communication with a heated zone 714. The heated zone 714 isincorporated with a convergent conduit nozzle eyelet or outlet 732.

In embodiments using a high-aspect ratio convergent extrusion nozzle, itmay be desirable to use a nozzle geometry that is optimized to preventthe buildup of feed material and/or to reduce the required feed pressureto drive the material through the nozzle outlet. For convenience herein,deposition heads which neck down creating fluid back pressure andextrude non-reinforced polymer material at a higher linear rate than thesupply of material are referred to as “extrusion nozzles” (according tothe conventional meanings of “extrude” and “nozzle”), while depositionheads for depositing core reinforced fiber according to the invention,which may not include any back pressure and deposit bonded ranks to apart at substantially the same linear rate as the filament is fed, arereferred to as “eyelets”. FIG. 21A shows a typical FFF extrusion nozzle800 including an inlet 806 that is aligned with an internal wall 802.The internal wall 802 extends up to a convergent section 804 that leadsto a nozzle outlet 808 with an area that is less than an area of theinlet 806. FIGS. 21B-21D depict various geometries including smoothtransitions to reduce a back pressure generated within the extrusionnozzle.

In one embodiment, as depicted in FIG. 21B, an extrusion nozzle 810includes an inlet 806 and an internal wall 812 with a first diameter.Initially, the internal wall 812 is vertical and subsequentlytransitions to a tangential inward curvature 814. After about 45 degreesof curvature, an inflection point 816 occurs and the internal wallreverses curvature and curves until the internal wall 812 is vertical.The resulting nozzle outlet 818 is aligned with the inlet 810, but has areduced second diameter. Additionally, the resulting exit flow from theoutlet will be aligned with the inlet flow, though flows through theoutlet that are not aligned with the inlet are also contemplated.

When a lower degree of alignment of polymer chains is desirable, thefirst inward curving section 814 depicted in FIG. 21B can be eliminated,such that the final geometry that turns the flow back into the extrudeddirection does so after a more typical chamfered inlet. One suchembodiment is depicted in FIG. 21C. As depicted in the figure, anextrusion nozzle 820 includes an internal wall that transitions to adownwards oriented curvature 822 directed towards the nozzle outlet 824.FIG. 4D depicts another embodiment in which an extrusion nozzle 826transitions to a standard chamfered nozzle section 828 which extends upto a point 830 where it transitions to a downwards oriented curvature832 to define a nozzle outlet 834. While particular nozzle geometrieshave been depicted in figures and described above, should be understoodthat other types of nozzle geometries might also be used as thedisclosure is not so limited.

In some embodiments, a deposition head includes one or more features toprevent drips. For example, a deposition head may include appropriateseals such as one or more gaskets associated with a printing nozzlechamber to prevent the inflow of air into the nozzle. This maysubstantially prevent material from exiting the deposition head untilmaterial is actively extruded using a feeding mechanism. In someinstances, it may be desirable to include other features to preventdripping from the deposition head as well while printing is stopped. Inone specific embodiment, a deposition head may include a controllableheater that can selectively heat the deposition head outlet toselectively start and stop the flow of material form the depositionhead. In this regard, a small amount of the resin near the outlet maysolidify when the heater is power is reduced to form a skin or smallplug to prevent drooling from the outlet. Upon reenergizing orincreasing the heater power, the skin/plug re-melts to allow the flow ofmaterial from the deposition head. In another embodiment, the depositionhead includes features to selectively reduce the pressure within thedeposition head to prevent dripping. This can be applied using a vacuumpump, a closed pneumatic cylinder, or other appropriate arrangementcapable of applying suction when nozzle dripping is undesirable. Thepneumatic cylinder is then returned to a neutral position, thuseliminating the suction, when printing is resumed. FIG. 22 depicts onesuch embodiment. In the depicted embodiment, an conduit nozzle 900 has amaterial 902 that is fed past one or more gaskets 910 and into a coldfeed zone 914 and heated zone 912 prior to exiting eyelet or outlet 908.An air channel 904 is connected to the cold feed zone 914 and is influid communication with a pneumatic cylinder 906. As depicted in thefigure, a gap is present between the material 902 and the cold feed zone914 through which air may pass. Therefore, the air channel 904 is influid communication with both the cold feed zone 914 as well as withmaterial located within the heated zone 912. During operation, thepneumatic cylinder 906 is actuated from a first neutral position to asecond position to selectively applying suction to the air channel 904when printing is stopped. Since the air channel 904 is in fluidcommunication with material within the heated zone 912, the suction maysubstantially prevent dripping of polymer melt located within the heatedzone. Once printing resumes, the pneumatic cylinder 906 may be returnedto the neutral position.

While various embodiments of deposition heads in cutting mechanisms aredescribed above, in some embodiments, it is desirable to use a towpreg,or other material, that does not require use of a cutting mechanism tocut. In view of the above, the inventors have recognized the benefitsassociated with using a material including a semi-continuous core strandcomposite with a three-dimensional printer. In such an embodiment, amaterial including a semi-continuous core has a core that has beendivided into plurality of discrete strands. These discrete strands ofthe core may either correspond to a solid core or they may correspond toa plurality of individual strands bundled together as the disclosure isnot so limited. Additionally, as described in more detail below, thesediscrete segments of the core may either be arranged such that they donot overlap, or they may be arranged in various other configurationswithin the material. In either case, the material may be severed byapplying a tension to the material as described in more detail below.The tension may be applied by either backdriving a feed mechanism of theprinter and/or translating a printer head relative to a printed partwithout depositing material from the deposition head.

In one embodiment a material including semi-continuous core includessegments that are sized relative to a melt zone of an associatedthree-dimensional printer nozzle such that the individual strands may bepulled out of the nozzle. For example, the melt zone could be at leastas long as the strand length of the individual fibers in a pre-pregfiber bundle, half as long as the strand length of the individual fibersin a pre-preg fiber bundle, or any other appropriate length. In such anembodiment, at the termination of printing, the material including asemi-continuous core is severed by tensioning the material. Duringtensioning of the material, the strands embedded in material depositedon a part or printing surface provide an anchoring force to pull out aportion of the strands remaining within the nozzle. When the individualstrands are appropriately sized relative to a melt zone of the nozzle asnoted above, strands that are located within both the extruded materialand with the nozzle are located within the melt zone of the nozzle.Consequently, when tension is applied to the material, the segmentslocated within the melt zone are pulled out of the melt zone of thenozzle to sever the material. In embodiments where longer strands areused, instances where at least some strands are pulled out of a moltenzone of the deposited material and retained within the nozzle are alsocontemplated. The above noted method may result in vertically orientedstrands of core material. These vertical strands may optionally bepushed over by the print head, or they are subsequently depositedlayers. By strategically placing vertically oriented strands within amaterial layer, it may be possible to increase a strength of theresulting part in the z direction by providing enhanced bonding betweenthe layers.

In another embodiment, a semi-continuous core embedded in acorresponding matrix material includes a plurality of strands that havediscrete, indexed strand lengths. Therefore, termination of thesemi-continuous core occurs at pre-defined intervals along the length ofthe material. Initially, since the terminations are located atpredefined intervals, the strand length may be larger than a length ofthe melt zone of an associated nozzle. For example, in one specificembodiment, a semi-continuous core might include individual strands, orstrand bundles, that are arranged in 3-inch lengths and are cleanlyseparated such that the fibers from one bundle do not extend into thenext. When using such a material, a three-dimensional printer may run apath planning algorithm to lineup breaks in the strand with naturalstopping points in the print. In this embodiment, there is a minimumfill size which scales with the semi continuous strand length becausethe printer cannot terminate the printing process until a break in thesemi-continuous strand is aligned with the conduit nozzle eyelet oroutlet. Therefore, as the strand length increases, in some embodiments,it may be advantageous to fill in the remainder of the layer with pureresin which has no minimum feature length. Alternatively, a void may beleft in the part.

In many geometries, the outer portion of the cross section provides morestrength than the core. In such cases, the outer section may be printedfrom semi-continuous strands up until the last integer strand will notfit in the printing pattern, at which point the remainder may be leftempty, or filled with pure resin.

In another embodiment, a material may include both of the aboveconcepts. For example, indexed continuous strands may be used, inparallel with smaller length bundles located at transition pointsbetween the longer strands, such that the melt zone in the nozzleincludes sufficient distance to drag out the overlapping strands locatedin the melt zone. The advantage of this approach is to reduce the weakpoint at the boundary between the longer integer continuous strands.During severance of a given core and matrix material, it is desirablethat the severance force is sufficiently low to prevent part distortion,lifting, upstream fiber breaking, or other deleterious effects. In somecases, strands may be broken during the extraction, which is acceptableat the termination point. While the strand length can vary based on theapplication, typical strand lengths may range from about 0.2″ up to 36″for large scale printing.

FIGS. 23A-24D depict various embodiments of a semi-continuous corefilament being deposited from a nozzle. As contrasted to the continuouscore filament 2 depicted in FIG. 24A.

As depicted in the FIG. 23A, a semi-continuous core filament 1000includes a first strand 1002 and a second strand 1004 located within thematrix material 1006. The semi-continuous core filament 1000 enters acold feeding zone 712 of a nozzle which is advantageously below theglass transition temperature of the matrix material. The semi-continuousmaterial 1000 subsequently flows through heated zone 714, sometimesreferred to as a melt zone. The matrix material 1006 present in thesemi-continuous material 1000 is melted within the heated zone 714 priorto deposition. Upon exit from the nozzle, semi-continuous core filament1000 is attached to a part or build platen 16 at anchor point 1005. Theseverance procedure can then occur in a number of ways. In oneembodiment, severance occurs by moving the print head forward relativeto the anchor point 1005, without advancing the semi-continuous corefilament 1000. Alternatively, the print head may remain stationary, andthe upstream semi-continuous core filament 1000 is retracted to applythe desired tension. Again by appropriately sizing the strand length toa length of the heated zone to ensure that an entire length of thestrand located within the nozzle is in the heated zone 714, the tensionprovided by the anchor point 1005 permits the remaining portion of thesecond strand 1004 located within the nozzle to pull the remnant of theembedded strand from the heated nozzle.

While FIG. 23A showed two individual strands, FIGS. 23B and 24B show asemi-continuous core filament 1008 including a distribution of similarlysized strands 1010 embedded in a matrix material 1006 and located in aprinter head similar to that described above. While three strands areshown in a staggered line, it should be understood that this is asimplified representation of a random, or staggered, distribution ofstrands. For example, material may include about 1,000 strands of carbonfiber (a 1 k tow). While a distribution of strand lengths 1015 andpositioning of the individual strands is to be expected, the strands 214may be sized and distributed such that there are many overlappingstrands of substantially similar length. By ensuring that heated zone714 is proportional to a strand length 1015, the fiber remnant can bemore easily pulled from the nozzle. For example, the strands that arelocated further downstream, i.e. mostly deposited within a part, willpull out from the nozzle easily. The strands that are mostly located inthe nozzle will most likely remain within the nozzle. The strands thatare half in the nozzle, and half out, will stochastically stay in thenozzle or get pulled out by the anchor point 1005 due to the roughlyequivalent forces being applied to roughly equivalent lengths of thestrands contained within the deposited material and the nozzle. Thevarious parameters of the conduit nozzle eyelet design such as thedesign of the cold feeding zone 714 and the conduit nozzle eyelet oroutlet transition as well as the viscosity of the polymer melt, thedegree of cooling of the printed semi-continuous core filament upon exitfrom the conduit nozzle eyelet or outlet, as well as other appropriateconsiderations will determine how the semi-continuous core filament issevered when a tension is applied to the material.

FIGS. 23C and 24C shows an indexed semi-continuous core filament 1012where the termination of the core material is substantially complete ateach section, thereby enabling clean severance at an integer distance.As depicted in the figures, the material includes individual sections ofone or more core segments 1014 embedded within a matrix material 1006.

The individual sections of core material are separated from adjacentsections of core material at pre-indexed locations 1016. Such anembodiment advantageously permits the clean severance of the material ata prescribed location. This is facilitated by the individual strands indifferent sections not overlapping with each other. This also enablesthe use of strand lengths that are larger than a length of theassociated heated zone 714 of the conduit nozzle eyelet. This alsopermits use of the smaller heated zone 714 in some embodiments. However,in addition to the noted benefits, since the individual strands indifferent sections do not overlap, the material will exhibit a reducedstrength at these boundary locations corresponding to the pre-indexedlocations 1016 depicted in the figures. FIG. 25 illustrates the use ofsuch a semi-continuous core filament. As depicted in the figure,multiple strands 1100 are deposited onto a part or build platen. Thestrands 1100 are deposited such that they form turns 1102 as well asother features until the print head makes it final pass and severs thematerial at 1104 as described above. Since the individual strands arelonger than the remaining distance on the part, the remaining distance1106 may either be left as a void or filled with a separate materialsuch as a polymer.

FIG. 24D shows an example of a hybrid approach between a semi-continuouscore filament and a continuous core filament. In the depictedembodiment, a material 1018 includes multiple discrete sectionsincluding one or more core segments 1014 embedded within a matrix 1006that are located at pre-indexed locations similar to the embodimentdescribed above in regards to FIGS. 24C and 25C. The material alsoincludes a continuous core 1020 embedded within the matrix 1006extending along a length of material. The continuous core 1020 may besized such that it may be severed by a sufficient tensile force toenable severing of the material at the pre-indexed locations simply bythe application of a sufficient tensile force. Alternatively, any of thevarious cutting methods described above might also be used.

While the above embodiments have been directed to materials that may besevered without the use of a cutting mechanism. It should be understoodthat semi-continuous core filaments may also be used with threedimensional printing systems including a cutting mechanism as thedisclosure is not so limited.

In traditional composite construction successive layers of compositemight be laid down at 0°, 45°, 90°, and other desired angles to providethe part strength in multiple directions. This ability to control thedirectional strength of the part enables designers to increase thestrength-to-weight ratio of the resultant part. Therefore, in anotherembodiment, a controller of a three dimensional printer may includefunctionality to deposit the reinforcing fibers with an axial alignmentin one or more particular directions and locations. The axial alignmentof the reinforcing fibers may be selected for one or more individualsections within a layer, and may also be selected for individual layers.For example, as depicted in FIG. 26 a first layer 1200 may have a firstreinforcing fiber orientation and a second layer 1202 may have a secondreinforcing fiber orientation. Additionally, a first section 1204 withinthe first layer 1200, or any other desired layer, may have a fiberorientation that is different than a second section 1206, or any numberof other sections, within the same layer.

The concept of providing axial orientation of the reinforcing fibers toprovide directional strength within the part may be taken further withthree dimensional printers. More specifically, FIGS. 27A-27C show amethod of additive manufacturing of an anisotropic object with a printerhead 1310, such as an electric motor or other part that may benefit fromanisotropic properties. In the depicted embodiment, a part 1300 has avertically oriented subcomponent 1302 that is printed with the partoriented with Plane A aligned with the XY print plane in a firstorientation. In this particular example, the printed material includes aconductive core such that the printed subcomponent 1302 forms a woundcoil of a motor. In the depicted embodiment, the coils are wound aroundthe Z direction. While a particular material for use in printing a motorcoil is described, it should be understood that other materials might beused in an anisotropic part for any number of purposes as the currentdisclosure is not limited to any particular material or application.

In order to form another coil, or other anisotropic subcomponent, on thepart 1300, a fixture 1304, shown in FIG. 27B, is added to the print areathough embodiments in which this feature is printed during, before, orafter the formation of part 1300 are also possible. In one embodiment,the fixture 1304 is positioned at, or below, the print plane 1306 and iscontoured to hold the part 1300 during subsequent deposition processes.The fixture may also include vacuum suction, tape, mechanical fasteners,printed snap fits, or any other appropriate retention mechanism tofurther hold the part during subsequent print processes.

After positioning the fixture 1304, the part 1300 is positioned onfixture 1304, which then holds the part 1300 in a second orientation,with plane A rotated to plane A′ such that the next subcomponent 1308can be added to the part 1300. The subcomponent 1308 is again depositedin the Z direction, but is out of plane with subcomponent 1302, as shownin FIG. 27C. While this example has been described with regards toforming the coiled windings of a motor, any anisotropic object could beformed using a series of fixture rotations of the part, or print head,to enable the continuous core reinforced filaments to be aligned in anoptimal direction for various purposes.

FIG. 28A shows the same anisotropic part as formed in the processdescribed in FIGS. 27A-27C, however, instead of making use of aplurality of fixtures, the three dimensional printer is capable ofrotating the part 1300 as well as the printer head 1310 about one ormore axes. As depicted in the figure, part 1300 is held in place by arotating axis 1312, which sets and controls the orientation of plane A.In FIG. 28B, rotating axis 1312 has been rotated by 90° to formsubcomponent 1308 in a direction that is perpendicular to subcomponent1302.

Conversely, printer head 510 could be pivoted about the XT and/or YTaxes to achieve a similar result. As FIGS. 28A-28B show, there are manyways to achieve anisotropic printing. Namely, the part may be moved androtated, the printer head may be moved and rotated, or a combination ofboth may be used to print an anisotropic part. It should be understood,that additional degrees of freedom could be added to either the rotationand movement of the part 1300 or the printer head 1310 based on themachine objectives, and part requirements. For example, in an automotiveapplication, rotating axis 1312 may correspond to a rotisserie, enablingrotation of the vehicle frame about the yT axis to enable continuousfibers to be laid in the X-Y plane, the Z-Y plane, or any plane inbetween. Alternatively, a fluid rotation following the external contoursof the vehicular body might be used to continuously deposited materialon the vehicle as it is rotated. Such a three dimensional printer mightoptionally add the XT axis to the printer head to enable full contourfollowing as well as the production of both convex and concave unibodystructures.

In addition to rotating the part 1300 and the printer head 1310, in someembodiments, a table 1314 supporting the part 1300 could be rotatedabout the ZT axis to enable spun components of a given fiber direction.Such an embodiment may provide a consistent print arc from the printhead to the part for core materials that have unique feeding anddeposition head requirements that prefer directional consistency.

In another embodiment, the core of a part may be built up as a series oftwo dimensional planes. The three-dimensional printer may then form, outof plane three dimensional shells over the interior core. The coresupports the shells which enables the shells to be constructed on theoutside of the core and may run up the sides of the part, over the top,and/or down the back sides of the part, or along any other location.Such a deposition method may aid in preventing delimitation and increasetorsional rigidity of the part due to the increased part strengthassociated with longer and more continuous material lengths. Furtherrunning the continuous fiber reinforced materials out of plane providesan out-of-plane strength that is greater than a typical bonded joint.

FIG. 29 shows a three dimensional printer head 1310 similar to thatdescribed above in regards to FIGS. 28A and 28B that can be used to forma part including a three dimensionally printed shell. The printer head1310 deposits any appropriate consumable material such as a continuouscore reinforced filament 2 onto the built platen 1314 in a series oflayers 1320 to build a part. The printer head 1310 is capable ofarticulating in the traditional XYZ directions, as well as pivoting inthe XT yT and zT directions. The additional degrees of freedom to pivotthe printer head 1310 allow the printer to create shells, and othercontiguous core reinforced out of plane layers, as well as twodimensional layers.

FIGS. 30A-30C depict various parts formed using the printer headdepicted in FIG. 29. FIG. 30A shows a part including a plurality ofsections 1322 deposited as two dimensional layers in the XY plane.Sections 1324 and 1326 are subsequently deposited in the ZY plane togive the part increased strength in the Z direction. FIG. 30B show arelated method of shell printing, where layers 1328 and 1330 are formedin the XY plane and are overlaid with shells 1332 and 1334 which extendin both the XY and ZY planes. As depicted in the figure, the shells 1332and 1334 may either completely overlap the underlying core formed fromlayers 1328 and 1330, see portion 1336, or one or more of the shells mayonly overly a portion of the underlying core. For example, in portion1338 shell 1332 overlies both layers 1328 and 1330. However, shell 1334does not completely overlap the layer 1328 and creates a steppedconstruction as depicted in the figure. FIG. 30C shows anotherembodiment where a support material 1340 is added to raise the partrelative to a build platen, or other supporting surface, such that thepivoting head of the three dimensional printer has clearance between thepart and the supporting surface to enable the deposition of the shell1342 onto the underlying layers 1344 of the part core.

The above described printer head may also be used to form a part withdiscrete subsections including different orientations of a continuouscore reinforced filament. For example, the orientation of the continuouscore reinforced filament in one subsection may be substantially in theXY direction, while the direction in another subsection may be in the XZor YZ direction. Such multi-directional parts enable the designer to runreinforcing fibers exactly in the direction that the part needsstrength.

The high cost of composite material has been one of the major barriersto widespread adoptions of composite parts. Therefore, in someembodiments a three dimensional printer may utilize a fill pattern thatuses high-strength composite material in selected areas and fillermaterial in other locations, see FIGS. 30D-30G. Consequently, incontrast to forming a complete composite shell on a part is describedabove, a partial composite shell is formed on the outer extremes of apart, to maximize the stiffness of the part for a given amount ofcomposite material used. Low-cost matrix material such as nylon plasticmay be used as the fill-in material, though other materials may also beused. Apart formed completely from the fill material 1350 is depicted inFIG. 30D. As illustrated in FIG. 30E, a composite material 1352 isdeposited at the radially outward most portions of the part andextending inwards for a desired distance to provide a desired increasein stiffness and strength. The remaining portion of the part is formedwith the fill material 1350. Alternatively, portions of the build planemay be left unfilled.

Depending on the desired strength and/or stiffness, a user may increaseor decrease an amount of the composite material 1352 used. This willcorrespond to the composite material extending either more or less fromthe various corners of the part. This variation in amount of compositematerial 1352 is illustrated by the series of figures FIGS. 30D-30G.

When determining an appropriate fill pattern for a given level ofstrength and stiffness, a control algorithm starts with a concentricfill pattern that traces the outside corners and wall sections of thepart, for a specified number of concentric infill passes, the remainderof the part may then be filled using a desired fill material. Theresultant structure maximizes the strength of the part, for a minimum ofcomposite usage. It should be understood that while the above process isdescribed for a two dimensional plane, it is also applicable to threedimensional objects as well.

FIGS. 31A-31C show the cross-sections of various embodiments of anairfoil with different fiber orientations within various subsections. Itshould be understood that while an airfoil as described below, thedescribed embodiments are applicable to other applications andconstructions as well.

FIG. 31A shows a method of building each section of the threedimensional part with plastic deposition in the same plane.Specifically, sections 1350, 1352 and 1354 are all constructed in thesame XY planer orientation. The depicted sections are attached at theadjoining interfaces, the boundary of which is exaggerated forillustration purposes. In another embodiment, and as depicted in FIG.31B, a part is constructed with separate sections 1362, 1364, and 1366where the fiber orientations 1368 and 1372 of sections 1362 and 1366 areorthogonal to the fiber orientation 1370 of section 1364. Byorthogonally orienting the fibers in section 1364 relative to the othersections, the resulting part has a much greater bending strength in theZ direction. Further, by constructing the part in this manner, thedesigner can determine the relative thickness of each section toprescribe the strength along each direction.

FIG. 31C depicts a shell combined with subsections including differentfiber orientations. In this embodiment, sections 1374, 1376, and 1378are deposited in the same direction to form a core, after which a shell1386 is printed in the orthogonal direction. The shell 1386 may be asingle layer or a plurality of layers. Further, the plurality of layersof shell 1386 may include a variety of orientation angles other thanorthogonal to the underlying subsections of the core, depending on thedesign requirements. While this embodiment shows the inner sections withfiber orientations all in the same direction 1380, 1382, and 1384, itshould be obvious that subsections 1374, 1376, and 1378 may be providedwith different fiber orientations similar to FIG. 31B as well.

In other embodiments, the continuous core reinforced filament, or otherappropriate consumable material, may require a post-cure, such that thepart strength is increased by curing the part. Appropriate curing may beprovided using any appropriate method including, but not limited to,heat, light, lasers, and/or radiation. In this embodiment, a part may beprinted with a pre-preg composite and subject to a subsequent post-cureto fully harden the material. In one specific embodiment, continuouscarbon fibers are embedded in a partially cured epoxy such that theextruded component sticks together, but requires a post-cure to fullyharden. It should be understood that other materials may be used aswell.

FIG. 32 depicts an optional embodiment of a three dimensional printerwith selectable printer heads. In the depicted embodiment, a print arm1400 is capable of attaching to printer head 1402 at universalconnection 1404. An appropriate consumable material 1406, such as acontinuous core reinforced filament, may already be fed into the printerhead 1402, or it may be fed into the printer after it is attached to theprinter 1400. When another print material is desired, print arm 1400returns printer head 1402 to an associated holder. Subsequently, theprinter 1400 may pick up printer head 1408 or 1410 which are capable ofprinting consumable materials that are either different in size and/orinclude different materials to provide different.

As depicted, such swappable printer heads are used one at a time, andadvantageously reduce the mass of the printer head and arm combination.This enables faster printing of a part due to the reduced inertia of theprinter head. In another embodiment, the print arm may have slots fortwo or more printer heads concurrently. Such heads may feed differentmaterial, apply printed colors, apply a surface coating of spaydeposited material, or the like. It should be understood that any numberof separate selectable print heads might be provided. For example, theprint heads may be mounted to a turret, with one print head in the“active” position and the others rotated out of position awaiting forthe appropriate time when they may be rotated into the print position.In another embodiment, print arm may 1400 pick up a vision system 1412for part inspection. Appropriate vision systems include cameras,rangefinders, or other appropriate systems.

While most of the above embodiments are directed to the use of preformedcontinuous core reinforced filaments, in some embodiments, thecontinuous core reinforced filament may be formed by combining a resinmatrix and a solid continuous core in the heated conduit nozzle. Theresin matrix and the solid continuous core are able to be combinedwithout the formation of voids along the interface due to the ease withwhich the resin wets the continuous perimeter of the solid core ascompared to the multiple interfaces in a multistrand core. Therefore,such an embodiment may be of particular use where it is desirable toalter the properties of the deposited material. Further, it may beespecially beneficial to selectively extrude one or more resin matrices,continuous cores, or a combination thereof to deposit variety of desiredcomposite structures.

FIG. 33 depicts a multi-element printer head 1500 that is capable ofselectively extruding material feed options 1502, 1504, and 1506 as wellas an optional cutting mechanism 8. More specifically, the multi-elementprinter head 1500 is capable of selectively depositing any of materialfeed options 1502, 1504, and 1506, as singular elements or incombination. It should be understood that other material feed optionsmay also be integrated with the multi-element printer head as thecurrent disclosure is not limited to any particular number of materialfeed options.

In one specific example of a multi-element printer head, material 1502is a continuous copper wire fed through a central channel. Further,material 1504 is a binding resin such as Nylon plastic and material 1506is a different binding resin such as a dissolvable support material. Themulti-element printer head 1500 is capable of extruding all the elementsat once where, for example, the copper wire 1502 might be surrounded bythe nylon binder 1504 on the bottom surface and the dissolvable supportmaterial 1506 on the top surface, see section 1508.

The multi-element printer head 1500 may also deposit the copper wire1502 coated with either the nylon binder 1504 or the soluble supportmaterial 1506 separately, see sections 1510 and 1514. Alternatively, themulti-element printer head 1500 can deposit the above noted materialoptions singly for any number of purposes, see the bare copper wire atsection 1512.

The ability to selectively deposit any of the one or more of thematerials in a given location as described above enables many advancedfunctionalities for constructing parts using three dimensional printingmethods. Also, the ability to selectively deposit these materialscontinuously also results in a significantly faster deposition process.It should be understood that while two specific resin materials and acore material have been described above, any appropriate resin and corematerial might be used and any number of different resins and coresmight be provided. For example, a single core and a single resin mightbe used or a plurality of cores and a plurality of resins might beprovided in the multi-element printer head.

In a related embodiment, the multi-element printer head 1500 includes anair nozzle 1508 which enables pre-heating of the print area and/or rapidcooling of the extruded material, see FIG. 33. The inclusion of the airnozzle 1508 enables the formation of structures such as flying leads,gap bridging, and other similar features. For example, a conductive corematerial may be extruded by the multi-element printer head 1500 with aco-extruded insulating plastic, to form a trace in the printed part. Theend of the trace may then be terminated as a flying lead. To achievethis, the multi-element printer head would lift, while commensuratelyextruding the conductive core and insulating jacket. The multi-elementprinter head may also optionally cool the insulating jacket with the airnozzle 1508. The end of the wire could then be printed as a “strippedwire” where the conductive core is extruded without the insulatingjacket. The cutting mechanism 8 may then terminate the conductive core.Formation of a flying lead in the above-noted manner may be used toeliminate a stripping step down stream during assembly.

The above embodiments have been directed to three dimensional printersthat print successive filaments of continuous core reinforced filamentin addition to pure resins and their core materials to create a threedimensional part. The position of continuous cores or fibers can also beused with three dimensional printing methods such as stereolithographyand selective laser sintering to provide three dimensional parts withcore reinforcements provided in selected locations and directions asdescribed in more detail below.

For the sake of clarity, the embodiment described below is directed to astereolithography process. However, it should be understood that theconcept of depositing a continuous core or fiber prior to or duringlayer formation can be applied to any number of different additivemanufacturing processes where a matrix in liquid or powder form tomanufacture a composite material including a matrix solidified aroundthe core materials. For example, the methods described below can also beapplied to Selective Laser Sintering which is directly analogous tostereolithography but uses a powdered resin for the construction mediumas compared to a liquid resin. Further, any of the continuous corefilaments noted above with regards to the continuous core reinforcedfilaments may be used. Therefore, the continuous cores might be used forstructural, electrical conductivity, optical conductivity, and/orfluidic conductivity properties.

In one embodiment, a stereolithography process is used to form a threedimensional part. In stereolithography, the layer to be printed istypically covered with resin that can be cured with UV light, a laser ofa specified wavelength, or other similar methods. Regardless of thespecific curing method, the light used to cure the resin sweeps over thesurface of the part to selectively harden the resin and bond it to theprevious underlying layer. This process is repeated for multiple layersuntil a three dimensional part is built up. However, in typicalstereolithography processes, directionally oriented reinforcingmaterials are not used which leads to final parts with lower overallstrength.

In order to provide increased strength as well as the functionalitiesassociated with different types of continuous core filaments includingboth solid and multistrand materials, the stereolithography processassociated with the deposition of each layer can be modified into atwo-step process that enables construction of composite componentsincluding continuous core filaments in desired locations and directions.More specifically, a continuous core or fiber may be deposited in adesired location and direction within a layer to be printed. Thedeposited continuous core filament may either be completely submerged inthe resin, or it may be partially submerged in the resin. After thecontinuous fiber is deposited in the desired location and direction, theadjoining resin is cured to harden around the fiber. This may either bedone as the continuous fiber is deposited, or it may be done after thecontinuous fiber has been deposited as the current disclosure is notlimited in this fashion. In one embodiment, the entire layer is printedwith a single continuous fiber without the need to cut the continuousfiber. In other embodiments, reinforcing fibers may be provided indifferent sections of the printed layer with different orientations. Inorder to facilitate depositing the continuous fiber in multiplelocations and directions, the continuous fiber may be terminated using asimple cutting mechanism, or other appropriate mechanism, similar tothat described above. In some applications, the same laser that is usedto harden the resin may be used to cut the continuous core filament.

FIG. 34 depicts an embodiment of the stereolithography process describedabove. As depicted in the figure, a part 1600 is being built on a platen1602 using stereolithography. The part 1600 is immersed in a liquidresin material 1604 contained in a tray 1606. The liquid resin materialmay be any appropriate photopolymer. In addition to the resin bath,during formation of the part 1600, the platen 1602 is moved tosequentially lower positions corresponding to the thickness of a layerafter the formation of each layer to keep the part 1600 submerged in theliquid resin material 1604. During the formation of each layer, acontinuous core filament 1608 is fed through a nozzle 1610 and depositedonto the part 1600. The nozzle 1610 is controlled to deposit thecontinuous core filament 1608 in a desired location as well as a desireddirection within the layer being formed. Additionally, in someembodiments, the feed rate of the continuous core filament 1608 is equalto the speed of the nozzle 1610 to avoid disturbing the alreadydeposited continuous core filaments. In the depicted embodiment, as thecontinuous core filament 1608 is deposited, a laser 1612, or otherappropriate type of electromagnetic radiation, is directed to cure theresin surrounding the continuous core filament 1608 in a location 1614behind the path of travel of the nozzle 1610. The distance between thelocation 1614 and the nozzle 1610 may be selected to allow thecontinuous core filament to be completely submerged within the liquidresin prior to curing as well as to avoid possible interference issuesby directing the laser 1612 at a location to close to the nozzle 1606.The laser is generated by a source 1616 and is directed by acontrollable mirror 1618. The three dimensional printer also includes acutting mechanism 1620 to enable the termination of the continuous corefilament as noted above.

In another embodiment of a stereolithography process, the depositedcontinuous core filament is held in place by one or more “tacks”. Thesetacks correspond to a sufficient amount of hardened resin material thatholds the continuous core filament in position while additional corematerial is deposited. The balance of the material can then be curedsuch that the cross linking between adjacent strands is maximized. Anynumber of different hardening patterns might be used to providedesirable properties in the final part. For example, when a sufficientnumber of strands has been deposited onto a layer and tacked in place,the resin may be cured in beads that are perpendicular to the directionof the deposited strands of continuous core filament. Curing the resinin a direction perpendicular to the deposited strands may provideincreased bonding between adjacent strands to improve the part strengthin a direction perpendicular to the direction of the deposited strandsof continuous core filament. While a particular curing pattern isdescribed, other curing patterns are also possible as would be requiredfor a desired geometry and directional strength.

FIG. 35 depicts one embodiment of the stereolithography processdescribed above. As depicted in the figure, the continuous core filament1608 is tacked in place at multiple discrete points 1622 by the laser1612 as the continuous core filament is deposited by a nozzle, notdepicted. After depositing a portion, or all, of the continuous corefilament 1608, the laser 1612 is directed along a predetermined patternto cure the liquid resin material 1604 and form the current layer.Similar to the above system, the laser, or other appropriateelectromagnetic radiation, is generated by a source 1616 and directed bya controllable mirror 1618. As illustrated by the figure, the liquidresin material 1604 may be cured in a pattern corresponding to lines1624 oriented perpendicular to the direction of the deposited strands ofcontinuous core filament 1608. Since the cure front is perpendicular tothe strands of continuous core filament 1608, the crosslinking betweenthe strands is increased.

It should be understood, that if separate portions of the layer includestrands of continuous core filament oriented in different directions,the cure pattern may include lines that are perpendicular to thedirection of the strands of continuous fibers core material in eachportion of the layer.

While a particular cure pattern with lines that are orientedperpendicular to the continuous fibers are described, other patterns arealso possible including cure patterns of lines that are orientedparallel to the continuous fibers as the current disclosure is notlimited to any particular orientation of the cure pattern.

Similar to the three dimensional printing processes described above withregards to depositing a continuous core reinforced filament, it may bedesirable to avoid the formation of voids along the interface betweenthe continuous core filament and the resin matrix during thestereolithography process in order to form a stronger final part.Consequently, it may be desirable to facilitate wetting of thecontinuous core filament prior to curing the liquid resin material. Insome embodiments, wetting of the continuous fiber may simply require aset amount of time. In such an embodiment, the liquid resin material maybe cured after a sufficient amount of time has passed and may correspondto a following distance of the laser behind the nozzle. In otherembodiments, the continuous core filament may be a continuousmultistrand core material. Such embodiment, it is desirable tofacilitate wicking of the liquid resin material between the multiplefilaments. Wetting of the continuous fiber and wicking of the resinbetween the into the cross-section of the continuous multistrand coremay be facilitated by maintaining the liquid resin material at anelevated temperature, using a wetting agent on the continuous fiber,applying a vacuum to the system, or any other appropriate method.

Having described several systems and methods for forming parts usingthree dimensional printing processes, as well as the materials used withthese systems and methods, several specific applications and componentsare described in more detail below.

In the simplest application, the currently described three dimensionalprinting processes may be used to form parts using composite materialswith increased structural properties in desired directions and locationsas described above. In another embodiment, optically or electricallyconductive continuous cores may be used to construct a part withinductors, capacitors, antennae, transformers, heat syncs, VIA's,thermal VIA's, and a plurality of other possible electrical and opticalcomponents formed directly in the part. Parts may also be constructedwith fluid conducting cores to form fluid channels and heat exchangersas well as other applicable fluidic devices and components.

In some embodiments, a part may also be constructed with sensors, suchas strain gauges, formed directly in the part to enable structuraltesting and structural health monitoring. For example, a cluster ofprinted copper core material can be added to a layer to forming a straingauge. Similarly, an optical fiber can be selectively added to the partfor structural monitoring reasons. Optical fibers can also be printed ina loop to form the coil of a fiber optic gyroscope with a plurality ofpossible advantages including longer loop lengths for increasedsensitivity as well as component integration and simplifiedmanufacturing. For example, the optical coil of the gyro can be printedinside of the associated external container, as part of a wing, orintegrated with any number of other parts. Additionally, an opticalfiber could be printed as part of a shaft encoder for an electricalmotor, which could also be formed using three dimensional printing.

FIG. 36 illustrates a printed part incorporating many of the componentsdescribed above that are formed directly in the part using the describedthree dimensional printing processes. The printed part 1700 includesprinted electrical traces 1702 for connecting the printed electricalcomponents as well as a printed inductor 1704 and a printed antennae1706 connected by the printed electrical traces 1702. The printed part1700 also includes a printed fiber optic cable 1708. Additionally,depending on the embodiment, the printed part 1700 may include contactsor leads, not depicted, for connecting other components such as chip1710 and connectors 1712 to the printed part.

FIGS. 37-39 depict the printing and formation process for a multilayerprinted circuit board (PCB) using additive manufacturing. As insubtractive PCB layout, a pattern of pads and traces can be designed,and then printed, as illustrated in the figures. However, the process ofadditive manufacturing of a PCB is simple enough to perform on a benchusing one machine, thereby enabling a substantial acceleration of thedesign cycle.

FIG. 37 depicts printing of a multi-layer PCB 1800, on a build platen16. The PCB 1800 is formed with a conductive core material 1802 and aninsulating material 1804 which are deposited using a printer headincluding a heated conduit nozzle 10 and cutting mechanism 8. Similar tothe multielement printer head described above, the conductive corematerial 1802 and insulating material 1804 may be selectively depositedeither individually or together.

Further, in some embodiments the conductive core material 1802 is solidto minimize the formation of voids in the deposited composite material.When the conductive core material 1802 is printed without the insulatingmaterial 1804 a void 1806 can be formed to enable the subsequentformation of vias for use in connecting multiple layers within the PCB1800. Depending on the desired application, the void 1806 may or may notbe associated with one or more traces made from the conductive corematerial 1802.

FIGS. 38 and 39 depict several representative ways in which thecurrently described three dimensional printer could be used to formvarious structures in a printed circuit board 1800. As above, theprinted circuit board 1800 can be printed with various combinations oftraces and voids. For example, voids 1812 are associated with a singlepiece of the conductive core material 1802 which acts as a trace. Thevoids 1812 are subsequently filled with solder or solder paste to formsolder pads 1814. In a similar fashion, the void 1816 is associated withtwo traces and can also be filled with solder or solder paste to form anelectrically connected via 1818 between two or more printed layers. Asan alternative to the above, a void 1820 may not be associated with atrace. Such a void may also be filled with solder or solder paste tofunction as a thermal via 1822. While the solder and/or solder paste maybe applied separately, in one embodiment, the solder fill can be doneusing an optional print head 1810 which is used to dispense solder or anequivalent electrical binding agent 1808. The solder may be applied as amolten solder, or as a solder paste for post processing thermal curingusing any appropriate technique. The ability to print various componentsand traces within a circuit board coupled with the ability to applysolder and/or solder paste, may help to further accelerate theprototyping process of a printed circuit board. In addition to theabove, separate components may be placed on the printed circuit board bythe same machine, another machine, or manually. Subsequently, theprinted circuit board can be heated to bond the separate components tothe printed circuit board and finish the part. It should be understoodthat while manufacturing processes for a printed circuit board describedabove, the ability to selectively form various structures within a threedimensional printed component can be used for any number of differentapplications.

The presently described three dimensional printing systems and methodsmay also be used to form composite structures. A schematicrepresentation of a composite structure is depicted in FIG. 41A whichshows a sandwich panel composite part. The top section 1900, and bottomsection 1902, are printed using a continuous core reinforced filament toform relatively solid portions. In contrast, the middle section 1904 maybe printed such that it has different properties than the top section1900 and the bottom section 1902. For example the middle section 1904may include multiple layers printed in a honeycomb pattern using acontinuous core reinforced filament, a pure resin, or even a threedimensionally printed foaming material. This enables the production of acomposite part including a lower density core using a three dimensionalprinter. Other composite structures that are not easily manufacturedusing typical three dimensional printing processes may also bemanufactured using the currently described systems, materials, andmethods.

While several different types of applications are described above, itshould be understood that the three dimensional printing systems andmaterials described herein may be used to manufacture any number ofdifferent structures and/or components. For example, thethree-dimensional printing systems and materials described herein may beused to manufacture airplane components, car parts, sports equipment,consumer electronics, medical devices, and any other appropriatecomponent or structure as the disclosure is not limited in this fashion

In addition to using the continuous core reinforced filaments to formvarious composite structures with properties in desired directions usingthe fiber orientation, in some embodiments it is desirable to provideadditional strength in directions other than the fiber direction. Forexample, the continuous core reinforced filaments might includeadditional composite materials to enhance the overall strength of thematerial or a strength of the material in a direction other than thedirection of the fiber core. For example, FIG. 41B shows a scanningelectron microscope image of a carbon fiber core material 2000 thatincludes substantially perpendicularly loaded carbon nanotubes 2002.Loading substantially perpendicular small fiber members on the coreincreases the shear strength of the composite, and advantageouslyincreases the strength of the resulting part in a directionsubstantially perpendicular to the fiber direction. Such an embodimentmay help to reduce the propensity of a part to delaminate along a givenlayer.

In traditional composites, fibers are laid up, then a hole is drilledafter the fact (subtractive machining). This is illustrated in FIG. 40Awhich illustrates multiple layers 1850, which may either be formed usingpure polymer filaments or core reinforced filaments. As also depicted inthe figure, a hole 1852 is subsequently formed in the part using adrilling or other appropriate machining process. In contrast, in someembodiments, a core reinforced filament 1854 is used to form a holedirectly in a part, see FIGS. 40B and 40C. More specifically, the corereinforced filament 1854 comes up to the hole, runs around it, thenexits from the direction it came, though embodiments in which thefilament exits in another direction are also contemplated. A benefitassociated with this formation method is that the hole is reinforced inthe hoop direction by the core in the core reinforced filament. Asillustrated in FIG. 40B, the core reinforced filament 1854 enters thecircular pattern tangentially. This is good for screws that will betorqued in. In another version, the core reinforced filament 1854 enterthe circular pattern at the center of the circle. Of course, it shouldbe understood that other points of entering the pattern are alsopossible. In one embodiment, the entrance angle is staggered in eachsuccessive layer (also described in a PPA). For example, if there aretwo layers, the entering angle of the first layer may be at 0 degreeswhile the entering angle for the second layer may be at 180 degrees.This prevents the buildup of a seam in the part. If there are 10 layers,the entering angle may be every 36 degrees or any other desired patternor arrangement.

As noted above, typical towpregs include voids, this may be due toconsiderations such as at a temperature and rate at which a greentowpregs pass through a nozzle as well as the difference in areas of thegreen and impregnated towpregs. Due to the relatively high-viscosity ofthermoplastics, for example, sections of the extruded material alsotypically are not fully wetted out. These “dry” weak points may lead topremature, and often catastrophic, component failure.

In view of the above, it is desirable to improve the wetting orimpregnating of towpregs during the impregnation step. One way in whichto do this is to pass a material including a core of one or more fibersand a matrix material through a circuitous path involving multiplechanges in direction of the material while the matrix material ismaintained in a softened or fluid state. For example, in the case of apolymer matrix, the polymer may be maintained at an appropriatetemperature to act as a polymer melt while the circuitous path functionsto mechanically work the matrix material into the fibers. This processmay help to reduce the processing time while enhancing the fiber wet-outto provide a substantially void free material. Moreover, reducing theresidence time of the matrix material, such as a thermoplastic matrixmaterial, at high temperature reduces degradation of the material whichresults in further strengthening of a resultant part formed using thecomposite material. The above noted process may be used for bothcontinuous, and semi-continuous, core materials.

In some embodiments, a circuitous path used to form a desired materialis part of a standalone system used to manufacture a consumablematerial. Alternatively, in other embodiments, a circuitous path isintegrated in the compression stage of a print head. In such anembodiment, friction within the print head may be minimized by using oneor more smooth walled guide tube with a polished surface. Further, theone or more guide tubes may be close-fitting relative to the material,such that the compressed fiber does not buckle and jam the print head.

FIG. 42 depicts one possible embodiment of a three-dimensional printerhead 2102 including a circuitous path impregnation system. In thedepicted embodiment, a continuous core filament 2100 is driven by a feedmechanism 2110 (e.g. the depicted rollers), into a cutting mechanism2104, through a receiving section 2106, and into a heated zone 2112 ofthe nozzle. When passing through the heated zone 2112, the continuouscore filament 2100 passes through a circuitous path 2108 correspondingto a channel that undergoes at least a first bend in a first directionand a second bend in a second direction prior to the material beingextruded from the nozzle into one or more layers 2116 on a print bed2118. The resulting shape of the circuitous path forms a somewhatsinusoidal path. However, it should be understood that any number ofbends and any desired curvature might be used to form the circuitouspath. Similar to the above noted printer heads, the printing process maybe controlled using a controller 2114 which may also control theimpregnation processes. The advantages associated with the depictedembodiment is provided by the back and forth mechanical motion of thecontinuous core filament 2100 within the circuitous path 4 which aids inthe impregnation of the input material.

FIG. 43A illustrates one possible embodiment of the continuous corefilament 2100 when it is input to the system. As illustrated in thefigure, the continuous core filament 2100 corresponds to a commingledgreen towpreg including one or more fibers 2120 bundled with a matrixmaterial 2122 in the form of fibers or particles. After passing throughthe heated zone and the circuitous path, the continuous core filament2100 has been fully wetted by the matrix material 2122 to provide asubstantially void free continuous core filament, see FIG. 43B.

In another embodiment, the circuitous path is provided by offset rollerswhich may either be stationary, or they may be constructed toadvantageously open during initial threading to provide a straightthrough path and subsequently close to provide the desired circuitouspath. FIGS. 44A and 44B show one possible implementation of such anembodiment.

As depicted in the figures, three or more rollers 204 are placed withinthe printer head 2102 to provide the desired circuitous path. Duringuse, the continuous core filament 2100 is fed through the offset rollersby the feeding mechanism 2110 and through the printer head. FIG. 44Bdepicts an optional loading strategy. In such an embodiment, the rollers2124 are selectively movable between a first position in which they forma circuitous path as illustrated in FIG. 44A and a second position inwhich they do not obstruct a path between an inlet and outlet of theprinter head 2102 in order to facilitate threading of the system withthe continuous core filament 2100, see FIG. 44B. After the material hasthreaded past the rollers 2124, they may return to the first position toform the circuitous path depicted in FIG. 44A.

In another embodiment, not depicted, a circuitous path located within aprint head is formed by a flexible tube such as apolytetrafluoroethylene tube. The flexible tube is selectively placed ina straight configuration to permit threading of the printer head.Subsequently, the flexible tube is deformed into a circuitous path afterthreading has been completed to facilitate impregnation of a continuouscore filament passing there through as described above.

In some instances, it is desirable to provide a fully wetted orimpregnated material to the feeding mechanism of a printer head. In suchan embodiment, a circuitous path wet-out of a continuous core filament2100 is performed as a pre-treatment step within the tension side of athree-dimensional printer, prior to feeding the resulting substantiallyvoid material into the compressive side of the three-dimensionalprinter, see FIG. 45. As depicted in the figure the continuous corefilament 2100 enters a pre-conditioner 2124. As noted above, whenentering the pre-conditioner 124, the continuous core filament 2100 maycorrespond to a comingled towpreg including one or more fibers andmatrix material. As the continuous core filament 2100 passes through thepre-conditioner 2124, it is heated and passes through a circuitous pathwhich may be provided by a set of offset rollers 2126, or otherappropriate configuration to facilitate impregnation of the material.After passing through the pre-conditioner 2124, the continuous corefilament 2100 passes through the feeding mechanism 2110 corresponding toa set of drive rollers. The feeding mechanism 2110 feeds the continuouscore filament 2100 into a print head 2130 including a vacuum pressuresystem 2132. The vacuum pressure system 2132, or other appropriatesystem, varies a pressure applied to the continuous core filament 2100within the print head. These pressure variations may facilitateimpregnation of the fibers and burst air pockets within the towpreg. Inanother preferred embodiment, a continuous vacuum line is used for thevacuum pressure system 2032 instead of the oscillating pump as depictedin the figure. Additionally, while a vacuum may be applied to vary apressure within the print head, embodiments in which positive pressuresare applied to the print head are also contemplated.

In yet another embodiment, the matrix material contained within a greencontinuous core filament is worked into the fibers by passing throughone or more compressive roller sets while the matrix is hot and capableof flowing. FIG. 46 shows one embodiment of a three-dimensional printhead 2034 including a first and second set of compression rollers 2136disposed within the print head. As depicted in the figure, thecontinuous core filament 2100 passes through the print head where it isheated and subjected to two subsequent compressions from the two sets ofcompression rollers. While two sets of rollers are depicted in thefigures, additional rollers within the print head may also be used.

In another embodiment, oscillating pressures and/or vacuums are used towork the matrix material into the fiber core of a continuous corefilament. Applying reduced pressures, or increased vacuums, to thematerial removes voids. Conversely, applying increased pressures, ordecreased vacuums, then forces the resin deeper into the fiber towpregas the air pressure around said towpreg increases. The above notedprocess may either be performed completely with vacuums, positivepressures, or a combination of the two as the disclosure is not solimited. For example, a material might be cycled between ambientpressure and a high pressure, between ambient pressure and a vacuum, orbetween positive pressures and vacuums.

In the above embodiments, mechanically working the matrix into the fibercores enables the production of substantially void free towpregs from avariety of starting materials. For example, comingled towpregs can beused. In an additional embodiment, a flat towpreg in which the polymermatrix is only partially wicked into the underlying fibers is subjectedto the circuitous path wetting method described above to wet out thetowpreg. In addition to enabling the manufacture of various types oftowpregs, if used as a pre-treatment, a precision extrusion die can beused to form the impregnated material into a desired size and shape forextrusion from a three dimensional printer. For example, the materialmay have a circular cross section though any other appropriately shapedcross section might also be used.

When desirable, a precision roller set can be used to maintain aconstant thickness along a relatively wider width of material outputfrom a print head 2102. Such an embodiment may be of use when dealingwith wider materials such as flat towpregs. FIG. 47 shows a print head2102 translating in a first direction. A nozzle 2136 of the print headis attached to a trailing compression roller 2138. The roller imparts acompressive force to the material deposited on to the onto print bed2140. Depending on the embodiment, the trailing roller 2138 canarticulate around the Z axis using any number of different mechanisms.For example, in one embodiment, the print head 2102 is free-rotating ona bearing, such that the roller always trails the direction of travel ofthe print head. In another embodiment, the entire print head 402 isconstructed to rotate. Alternatively, the print bed 2140 may be rotatedto achieve the desired trailing and displacement.

FIG. 48 shows one embodiment of a high-speed continuous core printercapable of using the above described materials. In the depictedembodiment, the printer includes a print arm 2200 including a pluralityof nozzles. The nozzles include a pure resin nozzle 2202 adapted toprint pure resin 2208. The print arm 2200 also includes a continuouscore filament nozzle 2204 adapted to print a continuous core filament2210 for use in fine detail work. Additionally, the print arm 2200includes a tape dispensing head 2206 capable of printing one or moreprintable tapes 2212. The tape dispensing head enables large infillsections to be printed quickly using the noted printable tapes. However,fine detail work and gaps that cannot be filled in by the tape can befilled by either the pure resin nozzle 2202 or continuous core filamentnozzle 2204 as the disclosure is not so limited. The above noted methodand system using wide tape fills greatly improves the speed of aprinter, enabling higher throughput, and commensurately lower cost.

As noted above, in some embodiments, it is desirable to provide amaterial with a smooth outer surface for a variety of reasons. Asdetailed below, the smooth outer surface, a desired shape, and/or adesired size may be obtained in a variety of ways.

In one embodiment, a core reinforced filament includes an internalportion including axially aligned continuous or semi-continuous fibers,or other materials, in the form of a tow, bundle, yarn, string, rope,thread, twine, or other appropriate form. The internal portion alsoincludes a matrix in which the fibers are embedded. The core reinforcedfilament also includes an external coating disposed on the internalportion of the filament. The external coating may be shaped and sized toprovide a desired cross-sectional shape and size. The resulting corereinforced filament may be used in a three dimensional printing processas described herein as well as other appropriate three dimensionalprinting processes as the disclosure is not so limited.

In a related embodiment, a method for manufacturing a core reinforcedfilament includes embedding a tow, bundle, yarn, string, rope, thread,cord or twine in a polymer matrix using any appropriate method. Theresulting filament is subsequently extruded with a polymer to form theexternal coating noted above. As described in more detail below, theexternal coating may be made from the same material, or a differentmaterial, as the matrix material of the internal portion of thefilament.

FIG. 49A depicts a process to make a fully-wetted or impregnated corereinforced filament with a smooth outer coating for use in athree-dimensional printing system. As depicted in the figure, acontinuous core element 2300 is pulled into a co-extrusion die 2302. Insome embodiments, the continuous core element 2300 is subjected tovarious pretreatments at 2301 prior to entering the co-extrusion die2302 as described in more detail below. Once introduced into theco-extrusion die 2302 the continuous core element 2300 is impregnatedwith matrix material 2306 at a mixing point 2304. Either during, orprior to wetting or impregnation of the continuous core element with thepolymer, an optional vacuum step may be employed to remove entrapped airfrom the continuous core filament. FIGS. 49B and 49C depict crosssectional views of various starting continuous core elements 2300 whichmay be towpregs including a plurality of aligned reinforcing fibers. Ascomplete wetting or impregnating is the primary goal of this step (asopposed to merely coating in traditional co-extrusion dies), thetemperature and pressure of the mixing step may be increased to achievethe desired full-wetting/impregnating through the fiber bundle.Alternatively, or in addition to the above, a circuitous path and/orvarying pressure may be applied as described above to further facilitatewetting/impregnation of the material.

As many carbon fiber and fiberglass towpregs are initially in atape-like format, the die exit 2308 of the co-extrusion die may act toconsolidate the continuous core element and polymer matrix material intoa desired shape and size to provide a smooth, constant diameter,composite filament. However, the filament will start to distortdown-stream of the coextrusion die as occurs with typical filamentmanufacturing processes. The inventors have recognized that thisdistortion is an artifact of cooling the extrusion without support whichis somewhat akin to ejecting an injection molded part too soon whichthen warps when outside of the mold.

Consequently, in some embodiments, a cooling tube 2312 and operativelycoupled cooling element 2310, such as a cooling jacket, are aligned withand support the extruded material. Consequently, the extruded corereinforced filament is permitted to cool while being constrained to adesired size and shape. Lubricating agents may advantageously be appliedto the filament upon entry to the tube, or at points along a length ofthe tube. The lubricating agents may either evaporate, or be washed offat the later time. The lubricants may function to reduce the draggingfriction of the core reinforced filament within the tube tosubstantially prevent, or at least reduce, “skipping” or surfaceroughness from dragging the filament through the cooling tube duringcooling. Depending on the core material, and its correspondingcompressibility and ductility, the cooling tube may be built with aseries of different inner diameter “dies” to achieve a desired shape andsize. Alternatively, a plurality of discrete “cooling dies” might beused in place of a cooling tube for certain materials. An output corereinforced material 2314 may exhibit cross sections similar to thosedepicted in FIGS. 49E-49F. Depending on the amount of compression usedin the cooling tube, or die, the material may exhibit varying crosssectional profiles that conform either more or less to a shape of thetube or die.

In some embodiments, the core reinforced filament is fed into a second,co-extrusion die 2316 where it is coated with another matrix material2318, such as a polymer or resin, prior to being output through the dieexit 2320 as a coated core reinforced filament 2322. This outer coating2326 is disposed on the internal portion 2324. The outer coating 2326may be made from the same material, or a different material, as thematrix material 2306 in the internal portion. Therefore, the outercoating 2326 may be selected to provide a desired performancecharacteristics such as bonding to previously deposited layers, wearresistance, or any other number of desired properties. Additionally, insome embodiments, the outer coating 2326 provides a smooth, fiber-freeouter diameter as shown in the cross-section is presented in FIGS.49G-491. FIG. 49G presents an embodiment of the core reinforced filamentincluding an internal portion 2324 and an outer coating 2326 formed withdifferent matrix materials as well as a plurality of filaments formingthe continuous core. FIG. 49H depicts an embodiment of the corereinforced filament including an internal portion 2324 and an outercoating 2326 formed with the same matrix material as well as a pluralityof filaments forming the continuous core. FIG. 491 presents anembodiment of the core reinforced filament including an internal portion2324 including a solid continuous core 2300. The inner and outer matrixmaterials may be any appropriate binder used in composites, including,but not limited to, thermoplastics, thermosets, resins, epoxies,ceramics, metals, waxes, and the like.

FIG. 50A depicts an alternative roller-based method to achievefull-wetting/impregnation of the fiber, combined with an outer coating.Similar to the above, the core material 2300 may have a cross-sectionsas depicted in FIGS. 50B and 50C. Additionally, the core material 2300may be subjected to an optional pre-treatment step at 2301. The corematerial 2300 is passed through a set of dispersion rollers 2330 whichare constructed and arranged to flatten the cross-section of the corematerial to a flattened cross-sectional shape 2332 illustrated in FIG.50D. Dispersing the individual fibers of the continuous core into aflattened shape may help to facilitate wetting/impregnation of thematrix material 2306 when it is introduced to the flattened continuouscore element 2332 at the mixing point 2304. Similar to the above, thecontinuous core element and matrix material may be subjected to acircuitous path and/or varying pressures to further facilitateimpregnation of the matrix material. Additionally, in the depictedembodiment, the system may optionally include a set of rollers 2334located downstream from the mixing point 2304. The rollers 2334 mayapply a force to the composite filament to further force the matrixmaterial 2306 into the continuous core element 2300. A cross-section ofthe resulting composite flattened tape 2336 is illustrated in FIG. 50E.The resultant flattened composite tape 2336 is subsequently fed into aforming die 2338. This step can either be achieved with a heated formingdie, that is heated to a sufficient temperature in order to reflow thematerial, or the forming die 2338 is located sufficiently close to theexit of the rollers 2334 such that the composite flattened tape is at asufficient temperature to be formed when entering the die. Again,similar to the above, an optional cooling tube 2312 and an associatedcooling element 2310 may be associated with the forming die 2338 inorder to support a cross-section of the core reinforced filament 2314 asit cools, see FIGS. 50E-50G. An outer coating may then be applied to thecourt reinforced filament to forming a coated core reinforced filament2322 as described above.

While the above described embodiments have been directed to the use of afully wetted, fully wicked material, that is substantially void free, itshould be noted that described outer coatings and impregnation methodsmay be used with materials including voids as well. Additionally, greenmaterials that have not been wetted might also be used with the threedimensional printers described herein. Further, while various shapessuch as flattened tapes and rounded cross-sectional profiles aredescribed above with regards to the manufacturing processes, anyappropriate shape of the material and/or resulting core reinforcedfilament is possible as the disclosure is not so limited.

The composition of the aforementioned two polymer matrix binders used inthe internal portion and outer coating of a composite filament maydiffer by one or more of the following factors: polymer molecularweight, polymer weight distribution, degree of branching, chemicalstructure of the polymer chain and polymer processing additives, such asplasticizers, melt viscosity modifiers, UV stabilizers, thermalstabilizers, optical brighteners, colorants, pigments or fillers.Manufacturing of core reinforced filaments with two different bindercompositions may be practiced in several different ways depending onwhich particular processing characteristic or the property of thefinished part one desires to modify or control.

In one embodiment, it is desirable to preserve the uniform distributionof the fibers in the interior portion of the filament and the circularcross section shape. In such an embodiment, the polymer matrix of theinterior portion may exhibit a higher melting point than the meltingpoint of the polymer matrix in the outer coating. Consequently, theinterior portion of the filament remains in a solid, or at least asemi-solid highly viscous state, when the external coating is applied.Correspondingly, the fibers contained within the continuous core willstay in place and the filament will retain its circular cross-sectionalshape during application of the outer coating polymer matrix byco-extrusion while avoiding migration of the continuous fibers throughthe molten matrix of the interior portion of the filament to the outercoating of the filament during the co-extrusion step.

In another embodiment, it is desirable to improve impregnation/wettingof the fiber towpreg by the matrix binder. Consequently, in someembodiments, a less viscous polymer melt is used as the matrix materialin the interior portion of the filament. Preferably, the polymer matrixmaterial used for the interior portion of the filament should have notonly low viscosity, but also exhibit improved interfacial wetting of thefiber surface. This may be obtained by matching the surface energy ofthe imbibing polymer melt with the surface energy of the continuousfiber material. The polymer matrix material used for the externalcoating may comprise a polymer with a higher melt viscosity than theinterior matrix polymer. The exterior polymer matrix material may alsoexhibit a lower melting point than the interior polymer. The wettingproperties of the outer coating matrix towards the continuous core is oflesser importance as the two should not in principle be in directcontact.

In yet another embodiment, is desirable to facilitate the adhesion of anexternal coating to the underlying bundle through the modification ofthe surface energy of the polymer melt and the continuous corefilaments. The surface energy can be controlled by a number of methods,including, but not limited to, varying the content and the type of thepolar groups in the polymer backbone, the addition of surface activecomponents to the melt, for example, surfactants, oils, inorganicfillers etc., exposing the fibers to electric gas discharge plasmas,chemical vapor deposition, ozone, or reactions with, or coating of,surface modifying compounds from solutions.

In another embodiment, surface energy modifiers may also be used tostrengthen the interlayer bonding of the filament as it is deposited bya three dimensional printer. For example, ozone may be deposited by theprint head to promote adhesion of a new layer to an existing layer. Inanother embodiment, the build chamber may be filled with a sufficientproportion of ozone to activate the exposed surfaces.

In yet another embodiment of the present invention, it may beadvantageous to improve the bond strength of freshly extruded fiber-richfilament to the underlying layer by selectively applying a stream ofheated vapor to a small area adjacent to, and/or just ahead of, thedeposition point of the freshly deposited filament.

In another embodiment, it is contemplated that the bond strength betweenthe freshly extruded fiber-rich filament and the underlying layer may beimproved by selectively directing a stream of air or another gasconsisting of a sufficient concentration of ozone toward a small areaadjacent to, and just ahead of, the deposition point of the freshlydeposited filament surface. Ozone readily reacts with the atomicallythick surface layers of organic polymers to create a multitude of polarreactive surface groups, such as hydroxyl, ozonide, peroxide,hydroperoxide, aldehyde and carboxylic groups, which by their veryreactive chemical and/or polar nature facilitate bonding of the surfacelayer to another material, such as ink, adhesive or another polymerbinder.

In yet another embodiment, it is desirable to increase the bondingstrength with a build platform to help prevent lifting off of a part, orsection of a part, from the build platform. Consequently, in someembodiments, a surface energy modifier is applied to the build platformto facilitate the adhesion of the extruded filament to said platform. Insome embodiments, the noted adhesion modification is used to increasethe adhesion of the first bonding layer to the build platform in a fewkey areas, such as the corners of a box, thereby causing greateradhesion where the part is most likely to peel up from the platform. Thecenter of the box, however, may be substantially free of surface energymodifiers to facilitate easy removal.

With regards to the above noted embodiments, it should be understoodthat the timing and/or quantity of deposited ozone, vapor, or othersurface energy modifier may be varied to obtain a desired level ofadhesion.

In another embodiment, a magnetic filler is loaded into the matrixmaterial. The magnetic filler may either be magnetically active, likeiron or steel, or it may be magnetized as the disclosure is not solimited. In the case of continuous core printing of electronics, themagnetic filler could be used to form a three dimensionally printedactuation members. Additionally, the magnetic matrix particles could beused to magnetically stick a part to a printing table during printing,and then release at the conclusion of printing. The magnetic materialmay either be integrated into a final part, or it may advantageously beintegrated into a removable support material with similar matrixexhibiting properties similar to the remainder of the material.

In yet another embodiment, the magnetically active filler particlesenable measurement and detection of the material, or support structure,using x-rays or metallic sensors. For example, using a materialincluding metallic powder in the support material, and not the modelmaterial, would enable easy detection of the removal of all the supportmaterial. In another embodiment, the magnetic material is added to apart, or all, of a part, to enable the detection of intricate featuresin x-ray detection, that would otherwise be invisible.

In some embodiments, a continuous core, such as continuous carbonfibers, is combined with a semi-aromatic polyamides and/or asemi-aromatic polyamide blends with linear polyamides which exhibitexcellent wetting and adhesion properties to the noted continuous carbonfibers. Examples of such semi-aromatic polyamides include blends ofsemi-aromatic and linear polyamides from EMS-Grivory, Domat/Ems,Switzerland, such as Grivory HT1, Grivory HT2, Grivory HT3 and othersimilar blends. By combining continuous reinforced fiber towpregs withhigh-temperature melting and fiber wetting polyamides and their blends,parts may be manufactured which are characterized by exceptionalmechanical strength and long-term temperature stability at usetemperatures 120 degrees C. and higher while ensuring extrudability ofthe composite tow, excellent fiber-matrix wettability, complete fibertowpreg permeation with the resin and excellent shear strength at thefiber-matrix interface.

The optional pre-treatments noted above are intended to facilitate fullwetting of the core material, and wicking of the matrix material intothe centers thereof. Various types of pretreatments can includecategories such as mechanical, rheology, and fiber-wettingpretreatments. The particular method(s) employed will depend on thematrix material chosen, and the core selected.

Appropriate mechanical pretreatments include, spreading the individualfibers of the core into a flattened ribbon-shaped towpreg by mechanicalor pneumatic means before contacting with the resin or melt (i.e. dipcoating). Alternatively, a towpreg may pass through a melt in a chamberthat is periodically evacuated to expand and remove air bubbles trappedbetween the fibers and to force the resin or melt into the interstitialspace between the fibers when the vacuum is released. Additionally,periodic cycles of higher air pressure may improve the effectiveness ofthe process by changing the size of entrapped air bubbles and forcingthe renewal of the air-fiber interface, thus, facilitating bubblemigration. Additionally, a resin or polymer milk may be injected fromone side of a continuous core such that it is injected through thecontinuous core as compared to simply surrounding it during atraditional coextrusion process. It should be understood that othermechanical pretreatments are also possible.

Appropriate rheological pretreatments of a continuous core include theuse of a low viscosity or high melt flow index resins or polymer melts.Additionally, polymers exhibiting low molecular weights and/or linearchains may be used. Polymers exhibiting a sharp melting point transitionwith a large change in viscosity might also be used. Such a transitionis a typical property exhibited by polyamides. Various features such asmultiple port melt injection, angled channels, as well as fluted orspiral-groove extrusion channel surface “morphologies” may be used toinduce higher melt turbulence and non-laminar melt flow which may resultin enhanced impregnation of the matrix material. Melt viscositymodifiers and lubricants used to lower the effective melt viscosity andimprove slip at the fiber surface might also be used.

Appropriate fiber wetting pretreatments may include precluding the fibersurfaces with a very thin layer of the same or similar polymer from adilute polymer solution followed by solvent evaporation to obtain alike-to-like interaction between the melt and the fiber surface. Polymeror resin solutions in neutral and compatible solvents can haveconcentrations from about 0.1 wt.-% to 1 wt.-% or higher. Additionally,one or more surface activation methods may be used to introduce orchange the polarity of the fiber surface and/or to introduce chemicallyreactive surface groups that would affect wetting/impregnation (contactangle) and adhesion (matrix-fiber interfacial shear strength) byphysically or chemically bonding the polymer matrix with the fibersurface. Several examples of suitable surface activation methodsinclude, but are not limited to: atmospheric pressure surface oxidationin air; air enriched in oxygen, nitrogen oxides, or other reactivegases, such as halogenated, sulfur, silicon or other volatile compounds;as well as a high-voltage corona discharges (a method widely used inactivating polyolefin film surfaces for printing). Low-pressure plasmaactivation techniques in air, oxygen, or the other gases enumeratedabove may also be used to introduce reactive chemical surface groupswith a chemical character defined by the process conditions (time,pressure, discharge energy (electrode bias voltage), residence time andthe composition of the reactive gas. The fiber surface may also bechemically activated using: activation methods in gas and liquid phase,such as silanization in the presence, of hexamethyldisilizane (HMDS)vapors, especially at elevated temperatures; and solvent-phase surfacemodification using organosilicon or organotitanium adhesion promoters,such as tris(ethoxy)-3-aminopropylsilane, tris(ethoxy) glycidyl silane,tetraalkoxytitanates and the like.

While the present teachings have been described in conjunction withvarious embodiments and examples, it is not intended that the presentteachings be limited to such embodiments or examples. On the contrary,the present teachings encompass various alternatives, modifications, andequivalents, as will be appreciated by those of skill in the art.Accordingly, the foregoing description and drawings are by way ofexample only.

What is claimed is:
 1. A three dimensional printer comprising: a supplyof a core reinforced filament having a solidified matrix materialimpregnating reinforcing strands aligned along the core reinforcedfilament; a filament drive configured to feed forward the corereinforced filament at a feed velocity; a print head including a nozzleconfigured to receive the core reinforced filament from the filamentdrive and heat the core reinforced filament in the nozzle as the corereinforced filament is translated through the nozzle, the nozzlecomprising a nozzle tip positioned to continuously iron the corereinforced filament as the core reinforced filament is translatedthrough the nozzle and fused into a part; a print bed configured toreceive the heated core reinforced filament translated through thenozzle; a print drive configured to relatively move the print head andprint bed; and a controller configured to control the print drive andfilament drive to relatively move the print head and the print bed at adeposition velocity matching the feed velocity of the core reinforcedfilament, and to apply pressure with the nozzle to continuously compactthe core reinforced filament as the core reinforced filament istranslated through the nozzle and deposited upon the print bed.
 2. Thethree dimensional printer according to claim 1, further comprising: acutter assembly configured to receive the core reinforced filament andcut the core reinforced filament at a temperature at which the matrixmaterial is unmelted.
 3. The three dimensional printer according toclaim 2, wherein the cutter assembly is located at a selected positionalong the path of the core reinforced filament between the filamentdrive and a nozzle outlet of the nozzle.
 4. The three dimensionalprinter according to claim 3, wherein the selected position is at alocation having a temperature below one of a melting temperature of thematrix and a glass transition temperature of the matrix.
 5. The threedimensional printer according to claim 1, wherein the nozzle furthercomprises a nozzle lip forming a smooth transition between a verticalpath and a horizontal path, and wherein the controller is furtherconfigured to control the print drive to position the nozzle lip toapply a compaction force while the nozzle heats the core reinforcedfilament to fuse at the nozzle.
 6. The three dimensional printeraccording to claim 1, wherein the filament drive is arranged andconstructed to allow a velocity of the core reinforced filament withinthe filament drive to exceed a speed at which the filament driveadvances the core reinforced filament.
 7. The three dimensional printeraccording to claim 1, wherein the print drive is arranged andconstructed to relatively maintain a tension along the reinforcingstrands of less than a force threshold of the filament drive and lessthan a force threshold at which fused filaments are pulled up from thepart.
 8. The three dimensional printer according to claim 1, whereinwithin the nozzle, the linear velocity of the matrix material and thelinear velocity of the reinforcing strands are substantially the same.9. The method according to claim 1, wherein the print head furthercomprises a receiving tube, the receiving tube being isolated from aheated portion of the nozzle by a thermal spacer that maintains thereceiving tube at a temperature in which the matrix material isunmelted.
 10. A three dimensional printer comprising: a supply of a corereinforced filament having a solidified matrix material impregnatingreinforcing strands aligned along the core reinforced filament; afilament drive configured to feed forward the core reinforced filament;a cutter assembly configured to receive the core reinforced filament andcut the core reinforced filament at a temperature at which the matrixmaterial is unmelted; a print head including a nozzle configured toreceive the core reinforced filament from the cutter and heat the corereinforced filament in the nozzle as the core reinforced filament istranslated out of the nozzle, the nozzle comprising a nozzle lip forminga smooth transition between a vertical feeding path and a horizontalprinting path; a print bed configured to receive the heated corereinforced filament translated through the nozzle; a print driveconfigured to relatively move the print head and the print bed; and acontroller configured to control the print drive and filament drive tocontrol a position of the nozzle lip to apply a compaction force whilethe nozzle heats the core reinforced filament and as the core reinforcedfilament is deposited upon the print bed.
 11. The three dimensionalprinter according to claim 10, wherein the cutter assembly is located ata selected position along the path of the core reinforced filamentbetween the filament drive and a nozzle outlet of the nozzle.
 12. Thethree dimensional printer according to claim 11, wherein the selectedposition is at a location having a temperature below one of a meltingtemperature of the matrix and a glass transition temperature of thematrix.
 13. The three dimensional printer according to claim 10, whereinthe nozzle lip is located at a distal end of the nozzle and isconstructed and arranged to continuously iron the core reinforcedfilament as the core reinforced filament is fused into a part.
 14. Thethree dimensional printer according to claim 10, wherein the nozzle lipis configured to reshape the core reinforced filament from an initialshape to a compacted shape.
 15. The three dimensional printer accordingto claim 14, wherein the nozzle lip is configured to reshape asubstantially circular distribution of reinforcing strands within theinitial shape to a substantially flattened, rectangular distribution ofreinforcing strands within the compacted shape.
 16. The threedimensional printer according to claim 10, wherein the print drive andthe filament drive are arranged and constructed to relatively maintain amatched velocity of deposition velocity of the core reinforced filamentupon the print bed and feed velocity of the core reinforced filament atthe filament drive.
 17. The three dimensional printer according to claim10, wherein the filament drive is arranged and constructed to allow afeed velocity at the filament drive to exceed a velocity at which thefilament drives the core reinforced filament.
 18. The three dimensionalprinter according to claim 10, wherein within the nozzle, the linearvelocity of the matrix material and the linear velocity of thereinforcing strands are substantially the same.
 19. The method accordingto claim 10, wherein the print head further comprises a receiving tube,the receiving tube being isolated from a heated portion of the nozzle bya thermal spacer that maintains the receiving tube at a temperature inwhich the matrix material is unmelted.
 20. A three dimensional printercomprising: a supply of a core reinforced filament having a solidifiedmatrix material impregnating reinforcing strands aligned along the corereinforced filament; a filament drive configured to feed forward thecore reinforced filament; a cutter assembly configured to receive thecore reinforced filament and cut the core reinforced filament at atemperature in which the matrix material is unmelted; a print headincluding a nozzle configured to receive the core reinforced filamentfrom the cutter and heat the core reinforced filament in the nozzle asthe core reinforced filament is displaced out of the nozzle; a print bedconfigured to receive the heated core reinforced filament translated outof the nozzle to form a part; and a print drive configured to relativelymove the print head and the print bed, the print drive and the filamentdrive being arranged and constructed to relatively apply a draggingforce at least via the reinforcing strands to drag forward the corereinforced filament through the nozzle without breaking the corereinforced filament.
 21. The three dimensional printer according toclaim 20, wherein the cutter assembly is located at a selected positionalong the path of the core reinforced filament between the filamentdrive and the nozzle outlet.
 22. The three dimensional printer accordingto claim 20, further comprising a receiving tube within the print headpositioned to receive a cut end of a core reinforced filament from thecutter assembly.
 23. The three dimensional printer according to claim20, further comprising a gap formed between an inlet tube and a guidetube of the cutter assembly and a shear configured to operate in the gapto sever the core reinforced filament, wherein after the core reinforcedfilament is severed, the core reinforced filament is configured to berethreaded by passing from the inlet tube across the gap to the outlettube.
 24. The three dimensional printer according to claim 20, furthercomprising a controller configured to control the print drive andfilament drive to apply pressure with the nozzle to continuously compactthe core reinforced filament as the core reinforced filament is fusedinto the part upon the print bed.
 25. The three dimensional printeraccording to claim 24, wherein the nozzle comprises a nozzle tippositioned to continuously iron the core reinforced filament as the corereinforced filament is fused into the part.
 26. The three dimensionalprinter according to claim 24, wherein the nozzle comprises a nozzle lipforming a smooth transition between a vertical path and a horizontalpath, the nozzle lip positioned to apply a compaction force while thenozzle heats the core reinforced filament to fuse at the nozzle.
 27. Thethree dimensional printer according to claim 20, wherein the filamentdrive is arranged and constructed to allow a feed velocity at thefilament drive to exceed a velocity at which the filament drives thecore reinforced filament.
 28. The three dimensional printer according toclaim 20, wherein within the nozzle, the linear velocity of the matrixmaterial and the linear velocity of the reinforcing strands aresubstantially the same.
 29. The method according to claim 20, whereinthe print head further comprises a receiving tube, the receiving tubebeing isolated from a heated portion of the nozzle by a thermal spacerthat maintains the receiving tube at a temperature in which the matrixmaterial is unmelted.